<PAGE>   1

                                                                    Exhibit 10.3

                                 FIRST AMENDMENT


     THIS FIRST AMENDMENT (the "Amendment") is made and entered into as of the
31st day of May, 2000, by and between EOP-RIVERSIDE PROJECT, L.L.C, A DELAWARE
LIMITED LIABILITY COMPANY ("Landlord") and ALLAIRE CORPORATION, A CORPORATION
ORGANIZED UNDER THE LAWS OF THE STATE OF DELAWARE ("Tenant").

                                   WITNESSETH

A.   WHEREAS, Landlord and Tenant are parties to that certain lease dated the
     23rd day of November, 1999 (the "Lease") for space currently containing
     approximately 270,446 square feet, consisting of 223,300 square feet in One
     Riverside Center (sometimes referred to as the "One Riverside Center
     Premises") and 47,146 square feet in Two Riverside Center (sometimes
     referred to as the "Two Riverside Center Premises"), all as further
     described in the Lease; and

B.   WHEREAS, Tenant has requested that additional space containing
     approximately 78,014 rentable square feet consisting of the 1st and 4th
     floors of Three Riverside Center (as defined in the Lease) as shown on
     EXHIBITS A-5 AND A-6 hereto (the "Three Riverside Center Premises") be
     added to the original Premises and that the Lease be appropriately amended
     and Landlord is willing to do the same on the terms and conditions
     hereinafter set forth;

     NOW, THEREFORE, in consideration of the mutual covenants and agreements
herein contained and other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, Landlord and Tenant agree as
follows:

I.   PREMISES. Section 1.A.(ii) is amended to provide that the Premises are
     located entirely in One Riverside Center, Two Riverside Center and Three
     Riverside Center. In addition, Section I.C. of the Lease is hereby deleted
     in its entirety and replaced by the following Section I.C.:

     I.C. "Premises" shall mean (i) the area shown on EXHIBITS A, A-1, A-2, A-3
     AND A-4 to the Lease and identified as Suites #1-100, #1-200, #1-300,
     #2-100, and #2-200 and (ii) the area shown on EXHIBITS A-5 AND A-6 hereto
     and identified as Suites #3-100 and #3-400. The Premises are located on
     floors one (1), two (2) and three (3) of One Riverside Center, floors one
     (1) and two (2) of Two Riverside Center and floors one (1) and four (4) of
     Three Riverside Center. The "Rentable Square Footage of the Premises" is
     deemed to be approximately 348,460 square feet, consisting of 223,300
     square feet in One Riverside Center (sometimes referred to as the "One
     Riverside Center Premises") and 47,146 square feet in Two Riverside Center
     (sometimes referred to as the "Two Riverside Center Premises") and 78,014
     square feet in Three Riverside Center (sometimes referred to as the Three
     Riverside Center Premises"). Landlord and Tenant acknowledge that Landlord
     has determined the location of the building management office on the first
     floor of Two Riverside Center as shown on EXHIBIT A-3 to the Lease. All
     corridors and restroom facilities located on floors one, two and three of
     One Riverside Center, floor two of Two Riverside Center, floor four of
     Three Riverside Center and any other floors leased by Tenant in their
     entirety (other than the first floor of Three Riverside Center) shall be
     considered part of the Premises. The total Rentable Square Footage of the
     Premises and of the Building has been determined from the approved permit
     set of construction drawings, without field measurement, based upon the
     1996 BOMA standard of measurement. Notwithstanding the foregoing, Landlord,
     at its sole cost and expense within six (6) months following the
     Substantial Completion (hereinafter defined) of the Base Building Work
     (hereinafter defined), shall cause the Rentable Square Footage of the
     Premises, the Rentable Square Footage of the Building and the Rentable
     Square Footage of the First Expansion Space (defined in Section IV of
     Exhibit E) to be field measured by an architect retained by Landlord. If,
     as a result of such field measurement, it is determined that the Rentable
     Square Footage of the Premises, First Expansion Space or the Rentable
     Square Footage of the Building has been misstated by more than 1%, Landlord
     and Tenant shall promptly enter into an amendment to this Lease to restate
     the Rentable Square Footage of the Building, First Expansion Space, and/or
     the Rentable Square Footage of the Premises, as the case may be, to reflect
     the actual


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     square footage pursuant to the field measurement. If such field measurement
     does not disclose a variance of 1% or more, any variance that is disclosed
     shall be considered by Landlord and Tenant to be immaterial and shall not
     result in an amendment of the Rentable Square Footage of the Building,
     First Expansion Space, and/or the Rentable Square Footage of the Premises,
     as the case may be. Landlord and Tenant acknowledge that the amendment of
     the Rentable Square Footage of the Premises will affect the Base Rent,
     Allowance (hereinafter defined), the Architectural and Engineering
     Allowance (hereinafter defined), Three Riverside Center Premises Allowance
     (hereinafter defined), the Three Riverside Center Premises Architectural
     and Engineering Allowance (hereinafter defined) as such amounts are
     determined on a "per square foot" basis. Landlord and Tenant further
     acknowledge that the amendment of either the Rentable Square Footage of the
     Premises or the Rentable Square Footage of the Building will affect
     Tenant's Pro Rata Share (as hereinafter defined)."

II.  BASE RENT. Section I.D. is hereby amended to add the following Base Rent
     schedule with respect to the Three Riverside Center Premises.

     "BASE RENT SCHEDULE FOR THE THREE RIVERSIDE CENTER PREMISES


<TABLE>
<CAPTION>

                        ANNUAL RATE          ANNUAL          MONTHLY
         PERIOD       PER SQUARE FOOT       BASE RENT       BASE RENT
         ------       ---------------       ---------       ---------
<S>      <C>          <C>                   <C>             <C>



</TABLE>


III. TENANT'S PRO RATA SHARE: Section I.E s hereby amended by deleting
     "54.6676%" and inserting "70.4372%" in lieu thereof.

IV.  BASE TAX YEAR AND BASE EXPENSE YEAR - The Tax Base Year and Expense Base
     Year for the Three Riverside Center Premises shall be the same as that for
     the remainder of the Premises. As such, the "Tax Base Year" shall be Fiscal
     Year 2001 and the "Expense Base Year" for the shall be the period beginning
     on the Commencement Date and ending on the day prior to the first
     anniversary of the Commencement Date.

V.   TERM. Section I.G. of the Lease is hereby deleted in its entirety and
     replaced by the following Section I.G:

     "I.G. "Term" shall mean the following with respect to the One Riverside
     Center Premises, Two Riverside Center Premises and Three Riverside Center
     Premises:

     TERM FOR THE ONE RIVERSIDE CENTER PREMISES

     A period of 120 months, as the same may be extended in accordance with the
     terms hereof. The "Term" for the One Riverside Center Premises shall
     commence on the later to occur of (1) July 1, 2000 (the "Target
     Commencement Date"); or (2) the date upon which Landlord Work in the One
     Riverside Premises is "Substantially Complete", as such date is determined
     pursuant to Section III.A. hereof (such date being referred to as the date
     of "Substantial Completion"); or (3) the date on which Landlord delivers
     full possession of the One Riverside Center Premises to Tenant (the later
     to occur of such dates being defined as the "Commencement Date"). The
     "Termination Date" shall,


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     unless sooner terminated as provided herein, mean the last day of the Term
     as the same may be extended as provided herein.

     TERM FOR THE TWO RIVERSIDE CENTER PREMISES

     A period of months, days and years, as the same may be extended in
     accordance with the terms hereof, commencing on the Two Riverside Center
     Premises Commencement Date (hereinafter defined) and ending on the
     Termination Date as determined above with respect to the One Riverside
     Center Premises, it being agreed that the entire Premises (i.e. the One
     Riverside Center Premises, Two Riverside Center Premises and Three
     Riverside Center Premises) shall always expire on the same date. The "Two
     Riverside Center Premises Commencement Date" shall occur on the later to
     occur of (1) August 1, 2000 (the "Two Riverside Center Target Commencement
     Date"); or (2) the date upon which Landlord Work in the Two Riverside
     Premises is "Substantially Complete", as such date is determined pursuant
     to Section III.A. hereof (such date being referred to as the date of
     "Substantial Completion"); (3) the date on which Landlord delivers full
     possession of the Two Riverside Center Premises to Tenant; or (4) the
     Commencement Date with respect to the One Riverside Center Premises.
     Landlord and Tenant acknowledge that the defined terms of "Substantially
     Complete" and "Substantial Completion" shall have the same meaning, but
     shall be applied separately, with respect to the One Riverside Center
     Premises and the Two Riverside Center Premises.

     Except as provided elsewhere in this Lease to the contrary, the adjustment
     of the Commencement Date and, accordingly, the postponement of Tenant's
     obligation to pay Rent shall be Tenant's sole remedy and shall constitute
     full settlement of all claims that Tenant might otherwise have against
     Landlord by reason of the Landlord Work in the One Riverside Center
     Premises not being Substantially Complete on the Target Commencement Date
     or the Two Riverside Center Premises not be Substantially Complete on the
     Two Riverside Premises Target Commencement Date. Landlord, in accordance
     with Section III.A. below, shall provide Tenant with notice of the date on
     which Landlord reasonably estimates that the Landlord Work will be
     Substantially Complete (as defined in Section III.A herein) in the One
     Riverside Center Premises and the Two Riverside Center Premises. Promptly
     after the determination of the Commencement Date and the Two Riverside
     Center Premises Commencement Date, Landlord and Tenant shall enter into a
     commencement letter agreement in the form attached as EXHIBIT C.

     TERM FOR THE THREE RIVERSIDE CENTER PREMISES

     A period of months, days and years, as the same may be extended in
     accordance with the terms hereof, commencing on the later to occur of (i)
     September 1, 2000, (ii) the Commencement Date with respect to the One
     Riverside Center Premises, or (iii) the date on which Landlord has
     Substantially Completed the Base Building Work in the Three Riverside
     Center Premises (the later of such dates being referred to as the "Three
     Riverside Center Commencement Date") and ending on the Termination Date as
     determined above with respect to the One Riverside Center Premises. It is
     understood that Tenant shall have the right to select the general
     contractor for the performance of Initial Alterations (hereinafter defined)
     in the Three Riverside Center Premises and that the substantial completion
     of the Initial Alterations shall not be a condition precedent to the
     occurrence of the Three Riverside Center Commencement Date."

VI.  THREE RIVERSIDE CENTER PREMISES - ADJUSTMENT OF COMMENCEMENT DATE;
     POSSESSION. Landlord and Tenant acknowledge and agree that Landlord is only
     obligated to perform Base Building Work in the Three Riverside Center
     Premises (and not Landlord Work as described in the Lease) and, as a result
     thereof, the terms and conditions of sections III.A through III.E of the
     Lease, including Tenant Delays and Late Completion Penalties, shall not
     apply to the Three Riverside Center Premises, and the following provisions
     are hereby added to Article III and shall govern with respect to the Three
     Riverside Center Premises:

     "F. The Base Building Work with respect to the Three Riverside Center
     Premises shall be deemed to be "Substantially Complete" on the date that
     all of the following conditions have been satisfied: (i) All of the Base
     Building Work with respect to the Three Riverside Center Premises has been
     performed (as evidenced by Landlord's


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     architect's certificate of substantial completion), other than any minor
     details of construction, mechanical adjustment or any other matter, the
     noncompletion of which does not materially interfere with Tenant's use and
     occupancy of the Three Riverside Center Premises as more particularly set
     forth below and in Section III.C. below ("Punchlist Items"), (ii) subject
     to the completion of Punchlist Items, the Base Building Work in the Common
     Areas of Three Riverside Center has been completed, including the
     installation of all elevators and stairways and the installation of all
     heating, ventilating, air-conditioning, fire/life safety, sanitary, water
     and power facilities; provided that Tenant shall be responsible for
     distributing any necessary systems to the Three Riverside Center Premises
     as part of the Initial Alterations; (iii) the ground floor lobby in the
     Building has been substantially completed, subject to Punchlist Items, and
     lobby furniture shall have been installed, (iv) there is adequate parking
     available to provide Tenant parking spaces at the Property based on a ratio
     of 3 spaces for each 1000 rentable square feet of Premises, (v) a cafeteria
     or other food service provider is open for business in the Building, (vi)
     workout facilities are open for use in the Building, and (vii) parking lot
     and outdoor lighting is installed and operational.

     From time to time upon request by Tenant or Tenant's designated
     representative, Landlord shall advise Tenant of the progress of the Base
     Building Work in the Three Riverside Center Premises and the approximate
     date on which Base Building Work in the Three Riverside Center Premises
     will be Substantially Complete.

     G. Within a reasonable time after the later to occur of the execution of
     this First Amendment and, with respect to the Terminable Space (hereinafter
     defined), the satisfaction of the Contingency (hereinafter defined),
     Landlord and Tenant shall conduct a walk through of the Three Riverside
     Center Premises for the purpose of preparing a list of Punchlist Items with
     respect to the Base Building Work in the Three Riverside Center Premises.
     Subject to the completion of any Punchlist Item, latent defects, and
     necessary corrections and adjustments to seasonal items such as heating and
     air conditioning that are not readily discoverable by Tenant on or about
     the date of Substantial Completion, by taking possession of the Three
     Riverside Center Premises for the purpose of performing the Initial
     Alterations, Tenant is deemed to have accepted the Three Riverside Center
     Premises and agreed that the Three Riverside Center Premises is in good
     order and satisfactory condition, with no representation or warranty by
     Landlord as to the condition of the Three Riverside Center Premises or the
     Building or suitability thereof for Tenant's use. However, nothing
     contained in this section shall be deemed to relieve Landlord from its
     obligation to complete, and Landlord shall complete, with reasonable speed
     and diligence, all Punchlist Items with respect to the Base Building Work.

     H. If Tenant takes possession of the Three Riverside Center Premises before
     the Three Riverside Center Premises Commencement Date, such possession
     shall be subject to the terms and conditions of this Lease and Tenant shall
     pay Rent (defined in Section IV.A.) to Landlord for each day of possession
     before the Three Riverside Center Commencement Date; provided, however,
     Tenant shall not be required to pay Rent for any days of possession before
     the Three Riverside Center Commencement Date unless Tenant shall be
     actively using the Three Riverside Center Premises for the conduct of
     Tenant's business. Notwithstanding anything herein to the contrary,
     Landlord agrees that Tenant shall have access to each portion of the Three
     Riverside Center Premises for the purpose of performing Initial Alterations
     following the later to occur of the execution of this First Amendment and,
     with respect to the Terminable Space, the satisfaction of the Contingency.

     I. In the event that Tenant terminates this Lease pursuant to subsections
     III.E.1 or III.E.3 above, such termination shall also apply with respect to
     the Three Riverside Center Premises."

VII. SECURITY DEPOSIT.

  A. The initial amount of the Security Deposit is hereby increased from
     $8,477,000.00 to $10,992,311.00. Within 15 days after the date on which
     Landlord notifies Tenant that the Contingency has been satisfied or the
     date on which this Amendment is terminated with respect to the Terminable
     Space, as the case may be, Tenant shall provide Landlord with cash or a
     letter of credit for the additional $2,445,311.00 (i.e. $10,922,311.00 -
     $8,477,000.00). Any portion of the initial $8,477,000.00 security deposit
     that has not, as of the date hereof, been delivered to Landlord shall
     remain


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     payable to Landlord in accordance with the terms and conditions of Section
     VI.A. of the Lease. Notwithstanding the foregoing, Landlord and Tenant
     acknowledge that the increased amount of the Security Deposit set forth
     above, as well as the Security Deposit and reduction amounts set forth
     below in the substitute Sections VI.C. and VI.D. are calculated based on
     the assumption that the Contingency will be satisfied and this Amendment
     shall remain in full force and effect with respect to the entire Three
     Riverside Center Premises. If the Contingency is not satisfied and this
     Amendment is terminated with respect to the Terminable Space, the
     applicable Security Deposit, reduction amounts and such other amounts as
     set forth in Section XI (Contingency) below will be adjusted as set forth
     in Section XI below.

  B. Sections VI.C and VI.D of the Lease are hereby deleted in their entirety
     and replaced with the following sections VI.C. and VI.D.:


     "C. Notwithstanding anything herein to the contrary, provided Tenant is not
     in default under this Lease as of the third (3rd) anniversary of the
     Commencement Date (i.e. the expiration of the 3rd lease year), the amount
     of the Security Deposit shall reduce from $10,992,311.00 to $8,582,758.00
     effective as of the 3rd anniversary of the Commencement Date. If the
     Security Deposit is provided by Tenant in the form of cash, Landlord shall
     return the reduced portion of the Security Deposit to Tenant within thirty
     (30) days following the 3rd anniversary of the Commencement Date. If the
     Security Deposit is provided in the form of a letter of credit, such
     reduction shall be accomplished by having Tenant provide Landlord with a
     substitute letter of credit in the reduced amount. If the Security Deposit
     is provided through a combination of cash and letter of credit, Tenant, by
     written notice to Landlord, shall advise Landlord as to the method that
     will be used to effectuate the reduction of the letter of credit.

     D. In addition to the reduction of the Security Deposit described in
     Section VI.C. above, the amount of the Security Deposit shall be subject to
     further reduction effective as of the 4th, 5th, 6th and 7th anniversaries
     of the Commencement Date (each referred to as an "Anniversary Date") as
     follows:

     1) If Tenant reported a profit for the 4 consecutive quarters immediately
     preceding the applicable Anniversary Date, the amount of the Security
     Deposit shall reduce by $1,560,502.00 effective as of such Anniversary
     Date. Such reduction shall be accomplished in the manner referred to in
     Section VI.C. above, provided that Landlord shall not be required to refund
     any portion of the Security Deposit or to accept a substitute letter of
     credit unless and until Tenant has provided Landlord with audited financial
     statements evidencing that Tenant is entitled to a reduction of the
     Security Deposit in accordance with the terms hereof.

     2) If Tenant did not report a profit for the 4 consecutive quarters
     immediately preceding the applicable Anniversary Date but did report a
     profit for 3 quarters within such period, the amount of the Security
     Deposit shall reduce by $780,251.00 effective as such Anniversary Date.
     Such reduction shall be accomplished in the manner referred to in Section
     VI.C. above, provided that Landlord shall not be required to refund any
     portion of the Security Deposit or to accept a substitute letter of credit
     unless and until Tenant has provided Landlord with audited financial
     statements evidencing that Tenant is entitled to a reduction of the
     Security Deposit in accordance with the terms hereof.

     3) If Tenant is not entitled to a reduction of the Security Deposit under
     D.1. or D.2. above, Tenant shall not be entitled to a reduction of the
     Security Deposit with respect to the applicable Anniversary Date. Tenant
     shall, however, be entitled to a reduction of the Security Deposit with
     respect to any future Anniversary Dates where the conditions for a
     reduction have been satisfied. Notwithstanding anything herein to the
     contrary, in no event shall the Security Deposit be reduced below the sum
     of: (i) $2,340,750.00, plus (ii) the amount of any increase in the Security
     Deposit pursuant to Section VI.E. below."

IX.  INITIAL ALTERATIONS.

  A. From and after the later to occur of the execution of this First Amendment
     and, with respect to the Terminable Space, the satisfaction of the
     Contingency, Tenant shall have access to the Three Riverside Center
     Premises for the purpose of performing


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     alterations and improvements in preparation for Tenant's occupancy thereof
     (the "Initial Alterations"). Notwithstanding the fact that Tenant has been
     provided with possession of the Three Riverside Center Premises, Tenant and
     its contractors shall not have the right to perform Initial Alterations in
     the Three Riverside Center Premises unless and until Tenant has complied
     with all of the terms and conditions of Article IX.C. of this Lease,
     including, without limitation, reasonable approval by Landlord of the final
     plans for the Initial Alterations and the contractors to be retained by
     Tenant to perform such Initial Alterations. Tenant shall be responsible for
     all elements of the design of Tenant's plans (including, without
     limitation, compliance with law, functionality of design, the structural
     integrity of the design, the configuration of the Three Riverside Center
     Premises and the placement of Tenant's furniture, appliances and
     equipment), and Landlord's approval of Tenant's plans shall in no event
     relieve Tenant of the responsibility for such design. Landlord agrees that
     Landlord shall not have any approval rights over the aesthetic aspects of
     the Initial Alterations unless the same are visible from the exterior of
     the Building or the interior of the Building atrium. Landlord's approval of
     the contractors to perform the Initial Alterations shall not be
     unreasonably withheld.

  B. Provided Tenant is not in default after the delivery of notice and the
     expiration of any applicable cure periods, Landlord agrees to contribute
     the sum of Two Million Three Hundred Forty Thousand Four Hundred Twenty and
     00/100 Dollars ($2,340,420.00) (i.e. $30 per rentable square foot of the
     Three Riverside Center Premises) (the "Three Riverside Center Premises
     Allowance") toward the cost of performing the Initial Alterations in
     preparation of Tenant's occupancy of the Three Riverside Center Premises.
     The Three Riverside Center Premises Allowance may only be used for the cost
     of labor, materials, permits and contractors fees in connection with the
     Initial Alterations. The Three Riverside Center Premises Allowance, less
     the amount of retainage provided for in Tenant's construction contract
     (which shall not be less than 5% nor more than 10%)(which retainage shall
     be payable as part of the final draw), shall be paid to Tenant or, at
     Landlord's option, to the order of the general contractor that performs the
     Initial Alterations, in periodic disbursements within thirty (30) days
     after receipt of the following documentation: (i) an application for
     payment and sworn statement of contractor substantially in the form of AIA
     Document G-702 covering all work for which disbursement is to be made to a
     date specified therein; (ii) a certification from an AIA architect
     substantially in the form of the Architect's Certificate for Payment which
     is located on AIA Document G702, Application and Certificate of Payment;
     (iii) Contractor's, subcontractor's and material supplier's waivers of
     liens which shall cover all Initial Alterations for the previous
     disbursement and all other statements and forms required for compliance
     with the mechanics' lien laws of the State of Massachusetts, together with
     all such invoices, contracts, or other supporting data as Landlord may
     reasonably require; and (iv) a request to disburse from Tenant containing
     an approval by Tenant of the work done and a good faith estimate of the
     cost to complete the Initial Alterations. In addition, prior to the first
     such disbursement, Tenant shall deliver to Landlord (x) a cost breakdown
     for each trade or subcontractor performing the Initial Alterations; (y)
     final plans and specifications for the Initial Alterations, together with a
     certificate from an AIA architect that such plans and specifications comply
     in all material respects with all laws affecting the Building, Property and
     Three Riverside Center Premises; and (z) copies of all construction
     contracts for the Initial Alterations, together with copies of all change
     orders, if any. Upon completion of the Initial Alterations, and prior to
     final disbursement of the Allowance, Tenant shall furnish Landlord with:
     (1) general contractor and architect's completion affidavits, (2) full and
     final waivers of lien, (3) receipted bills covering all labor and materials
     expended and used, (4) as-built plans of the Initial Alterations, and (5)
     the certification of Tenant and its architect that the Initial Alterations
     have been installed in a good and workmanlike manner in accordance with the
     approved plans, and in accordance with applicable laws, codes and
     ordinances. In no event shall Landlord be required to disburse the Three
     Riverside Center Premises Allowance more than one time per month. If the
     cost of the Initial Alterations exceeds the Three Riverside Center Premises
     Allowance, Tenant shall be entitled to the Three Riverside Center Premises
     Allowance in accordance with the terms hereof, but each individual
     disbursement of the Allowance shall be disbursed in the proportion that the
     Three Riverside Center Premises Allowance bears to the total cost for the
     Initial Alterations, less the retainage referenced above. Notwithstanding
     anything herein to the contrary, Landlord shall not be obligated to
     disburse any portion of the Three Riverside Center Premises Allowance
     during the continuance of an uncured default under the Lease, and
     Landlord's obligation to disburse shall only resume when and if such
     default is cured.



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<PAGE>   7


     In addition to Landlord's obligation to provide Tenant with an Three
     Riverside Center Premises Allowance, Landlord, provided Tenant is not in
     default after the delivery of notice and the expiration of any applicable
     cure periods, shall provide Tenant with an allowance (the "Three Riverside
     Center Premises Architectural and Engineering Allowance") in the amount of
     One Hundred Fifty Six Thousand Twenty Eight and 00/100 Dollars
     ($156,028.00) (i.e., $2 per rentable square foot of the Three Riverside
     Center Premises) to be applied toward the cost of architectural and
     engineering services for the Three Riverside Center Premises contracted by
     Tenant. Landlord shall disburse the Three Riverside Center Premises
     Architectural and Engineering Allowance, or applicable portion thereof, to
     Tenant within forty-five (45) days after Landlord's receipt of invoices and
     lien waivers from Tenant with respect to Tenant's actual engineering and
     architectural fees as described above. Any unused portion of the Three
     Riverside Center Premises Architectural and Engineering Allowance may be
     applied toward the cost of the Initial Alterations. Any unused portion that
     is not applied toward the cost of the Initial Alterations shall accrue to
     the sole benefit of Landlord, it being agreed that Tenant shall not be
     entitled to any credit, offset, abatement or payment with respect thereto.

  C. In no event shall the Three Riverside Center Premises Allowance be used for
     the purchase of moveable office equipment, furniture or other items of
     personal property of Tenant. In the event Tenant does not use the entire
     Three Riverside Center Premises Allowance in connection with the
     performance of the Initial Alterations, any unused amount shall accrue to
     the sole benefit of Landlord, it being understood that Tenant shall not be
     entitled to any credit, abatement or other concession in connection
     therewith. Tenant shall be responsible for all applicable state sales or
     use taxes, if any, payable in connection with the Initial Alterations
     and/or Three Riverside Center Premises Allowance.

  D. Landlord agrees to respond to any requests by Tenant for approval of its
     initial drafts of plans within ten (10) Business Days. Landlord agrees to
     respond to any requests by Tenant for approval of its contractors or any
     revisions to previously submitted plans within seven (7) Business Days.
     Notwithstanding the foregoing, the response times set forth above for the
     approval of any plans or revisions thereto shall be extended by five (5)
     additional Business Days in the event that the matters for which approval
     is being requested will, in Landlord's reasonable judgment, require review
     by an outside consultant. If Landlord shall disapprove any requests by
     Tenant, Landlord shall commit to writing its specific basis for such
     disapproval. Time is of the essence with respect to the response periods
     set forth herein.

  E. Landlord shall be responsible for performing the Base Building Work in the
     Three Riverside Center Premises as described in the Base Building Scope
     attached to the Lease as EXHIBIT M. All Base Building Work shall be
     performed at Landlord's sole cost and expense. In no event shall the cost
     of the Base Building Work be applied against or deducted from the Three
     Riverside Center Premises Allowance or Three Riverside Center Premises
     Architectural and Engineering Allowance. Notwithstanding the foregoing,
     Landlord shall have the right to change the plans and specifications for
     the Base Building Work from time to time, provided that Landlord shall not
     materially reduce the overall quality of the Base Building Work; provided,
     further, that Tenant shall have the right to approve any such changes that
     materially affect Tenant's occupancy, operation or design of the Three
     Riverside Center Premises, which approval shall not be unreasonably
     withheld or delayed.

  F. Tenant acknowledges that Landlord and its contractors, including ADP
     Marshall ("ADP") will be performing Base Building Work in the Building and
     Three Riverside Center Premises and improvement work in the premises of
     other tenants of the Building prior to and during the performance of the
     Initial Alterations by Tenant. Each portion of the Initial Alterations,
     including, without limitation, the delivery of any materials, the placement
     of dumpsters and sanitary facilities and the use of any loading docks must
     be coordinated with Landlord and ADP in advance in accordance with the
     rules and regulations enacted by Landlord and attached hereto as EXHIBITS
     B-1 and B-2. It is understood that Landlord is constructing the Base
     Building Work on a merit shop basis that is not restricted by the terms of
     a collective bargaining agreement. Notwithstanding the foregoing, Landlord
     hereby represents to Tenant and Tenant acknowledges that Landlord and ADP
     have reached an understanding with the New England Regional Council of
     Carpenters and the Laborers' International Union of North



                                       7
<PAGE>   8


     America, Local 560 with respect to the employment of union labor at the
     Building and that Tenant and Tenant's Contractor shall work diligently and
     in good faith with Landlord and ADP to comply with the understanding that
     was reached with such unions. Tenant and Tenant's Contractor shall be
     obligated to take all actions necessary to assure that the Initial
     Alterations are performed to completion without disruption to Landlord's
     performance of the Base Building Work from labor disputes arising from any
     cause, including, without limitation, disputes concerning union
     jurisdiction and the affiliation of workers employed by Tenant's Contractor
     or the subcontractors of Tenant's Contractor. Should a jurisdictional
     dispute arise, Tenant and Tenant's Contractor shall take the necessary
     legal steps required to allow Landlord's and ADP's construction of the Base
     Building Work to continue without interruption from any strikes, work
     stoppages or other actions in connection with the jurisdictional dispute.

  G. Once completed, the Initial Improvements shall be deemed "Leasehold
     Improvements" and the provisions of Section VIII.B. shall be applicable
     with respect to the Initial Alterations.

  H. Notwithstanding anything in Section X.A. to the contrary, Tenant, as part
     of the Initial Alterations, shall install any necessary sub-meters (as well
     as any electrical panels, transformers, bus duct plug and related
     equipment) in the Three Riverside Center Premises at Tenant's sole cost and
     expense (subject to the Three Riverside Center Premises Allowance).

X.   ASSIGNMENT AND SUBLETTING. All references in Article XII to One Riverside
     Center or Two Riverside Center shall be deemed to refer to One Riverside
     Center, Two Riverside Center or Three Riverside Center, or to One Riverside
     Center Premises or Two Riverside Center Premises shall be deemed to refer
     to One Riverside Center Premises, Two Riverside Center Premises or Three
     Riverside Center Premises. In addition, Landlord's rights under Section
     XII.B to recapture space that Tenant desires to Transfer shall not apply to
     any subleases or occupancy agreements for all or any portion of the Three
     Riverside Center Premises entered into by Tenant during the first 15 months
     of the Term and having a term not exceeding four (4) years ("Initial Three
     Riverside Subleases").

XI.  CONTINGENCY. Landlord and Tenant acknowledge that, with the exception of
     the 25,117 rentable square feet shown on EXHIBIT A-7 hereto (the
     "Unencumbered Space"), the Three Riverside Center Premises is currently
     leased to Harvard Vanguard Medical Associates, Inc. ("Harvard") pursuant to
     the terms and conditions of a lease dated December 15, 1999 (the "Harvard
     Lease"). The 52,897 rentable square foot portion of the Three Riverside
     Center Space that is leased to Harvard is referred to herein as the
     "Terminable Space". Landlord is currently engaged in good faith
     negotiations with Harvard with respect to a termination of the Terminable
     Space (the "Harvard Termination"). Tenant acknowledges and agrees that (i)
     there is no guaranty that Landlord and Harvard will enter into the Harvard
     Termination, (ii) Landlord shall be under no obligation to enter into the
     Harvard Termination, and (iii) this First Amendment, with respect to the
     Terminable Space only, is contingent upon Landlord and Harvard entering
     into the Harvard Termination (the "Contingency"). In the event that
     Landlord and Harvard do not enter into the Harvard Termination by May 12,
     2000, either party shall have the right to terminate this First Amendment
     with respect to the Terminable Space only by written notice to the other on
     or before the date on which the Contingency is satisfied. If either party
     elects to terminate this Amendment with respect to the Terminable Space,
     this Amendment shall continue in full force and effect subject to the
     following:

     1)   The Three Riverside Center Premises shall refer only to the 25,117
          rentable square feet shown on Exhibit A-7 and the Rentable Square
          Footage of the Premises shall be 295,563 square feet;

     2)   The Annual Base Rent and Monthly Base Rent for the Three Riverside
          Premises shall be appropriately adjusted based on the new Three
          Riverside Premises square footage (i.e. 25,117);

     3)   Tenant's Pro Rata Share shall be 59.7447%;

     4)   The Security Deposit shall be increased from $8,477,000.00 to
          $9,264,000.00. As such, the additional amount to be provided by Tenant
          shall be $787,280.00. In


                                       8

<PAGE>   9


          addition, Sections VI.C. and VI.D. of the Lease shall be deleted in
          their entirety and replaced with the following sections VI.C. and
          VI.D:

          "C. Notwithstanding anything herein to the contrary, provided Tenant
          is not in default under this Lease as of the third (3rd) anniversary
          of the Commencement Date (i.e. the expiration of the 3rd lease year),
          the amount of the Security Deposit shall reduce from $9,264,280.00 to
          $7,279,876.00 effective as of the 3rd anniversary of the Commencement
          Date. If the Security Deposit is provided by Tenant in the form of
          cash, Landlord shall return the reduced portion of the Security
          Deposit to Tenant within thirty (30) days following the 3rd
          anniversary of the Commencement Date. If the Security Deposit is
          provided in the form of a letter of credit, such reduction shall be
          accomplished by having Tenant provide Landlord with a substitute
          letter of credit in the reduced amount. If the Security Deposit is
          provided through a combination of cash and letter of credit, Tenant,
          by written notice to Landlord, shall advise Landlord as to the method
          that will be used to effectuate the reduction of the letter of credit.

          D. In addition to the reduction of the Security Deposit described in
          Section VI.C. above, the amount of the Security Deposit shall be
          subject to further reduction effective as of the 4th, 5th, 6th and 7th
          anniversaries of the Commencement Date (each referred to as an
          "Anniversary Date") as follows:

          1) If Tenant reported a profit for the 4 consecutive quarters
          immediately preceding the applicable Anniversary Date, the amount of
          the Security Deposit shall reduce by $1,323,614.00 effective as of
          such Anniversary Date. Such reduction shall be accomplished in the
          manner referred to in Section VI.C. above, provided that Landlord
          shall not be required to refund any portion of the Security Deposit or
          to accept a substitute letter of credit unless and until Tenant has
          provided Landlord with audited financial statements evidencing that
          Tenant is entitled to a reduction of the Security Deposit in
          accordance with the terms hereof.

          2) If Tenant did not report a profit for the 4 consecutive quarters
          immediately preceding the applicable Anniversary Date but did report a
          profit for 3 quarters within such period, the amount of the Security
          Deposit shall reduce by $661,807.00 effective as such Anniversary
          Date. Such reduction shall be accomplished in the manner referred to
          in Section VI.C. above, provided that Landlord shall not be required
          to refund any portion of the Security Deposit or to accept a
          substitute letter of credit unless and until Tenant has provided
          Landlord with audited financial statements evidencing that Tenant is
          entitled to a reduction of the Security Deposit in accordance with the
          terms hereof.

          3) If Tenant is not entitled to a reduction of the Security Deposit
          under D.1. or D.2. above, Tenant shall not be entitled to a reduction
          of the Security Deposit with respect to the applicable Anniversary
          Date. Tenant shall, however, be entitled to a reduction of the
          Security Deposit with respect to any future Anniversary Dates where
          the conditions for a reduction have been satisfied. Notwithstanding
          anything herein to the contrary, in no event shall the Security
          Deposit be reduced below the sum of: (i) $1,985,420.00, plus (ii) the
          amount of any increase in the Security Deposit pursuant to Section
          VI.E. below."

     5)   The amount of the Three Riverside Premises Allowance shall be
          $753,510.00 and the amount of the Three Riverside Premises
          Architectural and Engineering Allowance shall be $50,234.00; and

     6)   Tenant's parking spaces shall be allocated as follows: 626 spaces in
          the parking structure, 185 spaces in the surface parking areas and 76
          spaces in the executive parking garage

XII. PARKING. Section VI.A of Exhibit E to the Lease is hereby deleted and
     replaced with the following Section VI.A:

     "A. During the initial Term, Landlord shall make parking spaces available
     to Tenant at the Property based on a ratio of 3 parking spaces per 1,000
     rentable square feet of Premises leased by Tenant from time to time (the
     "Parking Ratio"). Tenant acknowledges that handicapped parking spaces and
     visitor parking spaces are included within the Parking Ratio of 3 spaces
     per 1,000 rentable square feet. In other



                                       9

<PAGE>   10


       words, Tenant's Pro Rata Share of the total amount of visitor and
       handicapped parking spaces for the entire Property shall be deducted from
       the number of parking spaces that Tenant is entitled to use based on the
       Parking Ratio. Landlord, in its sole discretion, shall have the right to
       allocate Tenant's parking rights between the surface parking areas, the
       parking structure and the executive parking garage beneath One Riverside
       Center (collectively referred to at the "Parking Areas"), provided that
       not less than 89 of Tenant's parking spaces (exclusive of handicapped
       parking spaces) shall be located in the executive parking garage beneath
       the Building. As of the date hereof, it is contemplated that Tenant's
       parking spaces will be allocated as follows: 738 spaces in the parking
       structure, 218 spaces in the surface parking areas and 89 spaces in the
       executive parking garage. Tenant shall not have the right to lease or
       otherwise use more than its share of parking spaces. Landlord shall have
       the right to establish such rules and regulations as Landlord reasonably
       elects to monitor the use of parking spaces by Tenant and other tenants,
       visitors and invitees and to assure, to the extent reasonably possible,
       that such parties are parking in the specific areas (e.g. surface areas,
       parking structure or garage) designated by Landlord and Tenant is not
       exceeding the Parking Ratio. Without limitation, Landlord shall have the
       right to implement a system of parking passes, parking stickers, card key
       access or any other system reasonably designated by Landlord. Tenant
       shall be responsible for assuring that its visitors, employees,
       subtenants and invitees comply with the rules and regulations designated
       by Landlord. Landlord shall have the right to require Tenant to institute
       and operate a subsidized MBTA pass program at the Premises to encourage
       Tenant's employees to use public transportation."

XIII.  MONUMENT SIGN. Section VIII of Exhibit E to the Lease is hereby amended
       by adding the following sentence: "Notwithstanding anything herein to the
       contrary, Initial Three Riverside Subleases (as defined in Section XII of
       the Lease) shall not be taken into account for purposes of determining
       whether the Monument Signage Conditions have been satisfied."

XIV.   DIRECTORY AND ENTRY SIGNAGE. Section IX.A of Exhibit E to the Lease is
       hereby amended by adding the following sentence: "Notwithstanding
       anything herein to the contrary, Landlord shall not have any right to
       remove, nor require the removal of, the Atrium Sign because the existence
       of Initial Three Riverside Subleases (as defined in Section XII of the
       Lease) shall cause Tenant to be in violation of the sublease restrictions
       and/or occupancy requirements of this Section."

XV.    PARKING STRUCTURE SIGNAGE. Section X of Exhibit E to the Lease is hereby
       amended by adding the following subsection: "D. Notwithstanding anything
       herein to the contrary, Landlord shall not have any right to remove, nor
       require the removal of, the Parking Structure Sign because the existence
       of Initial Three Riverside Subleases (as defined in Section XII of the
       Lease) shall cause Tenant to be in violation of the sublease restrictions
       and/or occupancy requirements of this Section. In addition, Initial Three
       Riverside Subleases shall not be taken into account for purposes of
       determining whether the Parking Signage Conditions have been satisfied."

XVI.   ONE RIVERSIDE SIGNAGE. Section XI of Exhibit E to the Lease is hereby
       amended by adding the following subsection: "D. Notwithstanding anything
       herein to the contrary, Landlord shall not have any right to remove, nor
       require the removal of, the One Riverside Center Sign because the
       existence of Initial Three Riverside Subleases (as defined in Section XII
       of the Lease) shall cause Tenant to be in violation of the sublease
       restrictions and/or occupancy requirements of this Section. In addition,
       Initial Three Riverside Subleases shall not be taken into account for
       purposes of determining whether the Riverside Center Signage Conditions
       have been satisfied."

XVII.  THREE RIVERSIDE SIGNAGE. Section XII of Exhibit E to the Lease is hereby
       amended as follows:

       a.     The following subsection is hereby added: "C. Notwithstanding
              anything herein to the contrary, Landlord shall not have any right
              to remove, nor require the removal of, the Three Riverside Center
              Sign because the existence of Initial Three Riverside Subleases
              (as defined in Section XII of the Lease) shall cause Tenant to be
              in violation of the sublease restrictions and/or occupancy
              requirements of this Section. In addition, Initial Three Riverside
              Subleases shall not be taken into account for purposes of
              determining whether the Riverside Center Signage Conditions have
              been satisfied."


                                       10

<PAGE>   11


       b.     Section XII.A and XII.B are hereby amended as follows: (i) the
              words "fifty percent (50%) of the total rentable square footage of
              Three Riverside Center" are hereby deleted and replaced with
              "75,000 rentable square feet in Three Riverside Center"; and (ii)
              the words "50% of the total rentable square footage of Three
              Riverside Center" in subsection XII.A(4) and XII.B(6) are hereby
              deleted and replaced with "75,000 rentable square feet in Three
              Riverside Center". Landlord acknowledges that, provided this
              Amendment is not terminated with respect to the Terminable Space,
              Tenant has satisfied the Three Riverside Center Signage Condition
              with respect to the amount of space leased by Tenant in Three
              Riverside Center. Such condition will be deemed to have been
              satisfied regardless of whether a remeasurement pursuant to
              Section I.C. of the Lease causes the square footage of the Three
              Riverside Center Premises to drop below 75,000 rentable square
              feet.

XVIII. SUPPLEMENTAL HVAC UNITS AND ANTENNA/DISHES. Section XIII of Exhibit E to
       the Lease is hereby amended by increasing the number of Roof Top Units
       from ten (10) to thirteen (13).

XIX.   BUILDING RISERS. Section XVII of Exhibit E to the Lease is hereby deleted
       and replaced with the following Section XVII:

       "XVII. BUILDING RISERS. Tenant shall have the right to use the vertical
       sleeves in One Riverside Center, Two Riverside Center and Three Riverside
       Center for Tenant's data and telecommunication cabling and in connection
       with the rights granted to Tenant with respect to the Roof Space. Tenant,
       acknowledges, however, that the existing vertical sleeves run to the top
       floor of the Building, but not through to the roof of the Building. As
       such, if Tenant desires to have the sleeves run to the roof, Tenant will
       be responsible for any costs required to extend the sleeves through to
       the roof or to install separate sleeves connecting the top floor of the
       Building to the roof. All such usage shall be in common with Landlord and
       shall not adversely affect Landlord's right to use the vertical sleeves
       for the operation of the Building (including the leasing, licensing and
       granting of roof rights to third parties); provided that Landlord shall
       not lease, license or grant any roof rights to third parties to the
       extent that the same would have an adverse affect on Tenant's ability to
       use the vertical sleeves in connection with the normal operation of
       Tenant's business in the Premises. Landlord, at Landlord's expense, has
       installed for Tenant's use, conduits within the Building to facilitate
       Tenant's ability to interconnect Tenant's systems within One Riverside
       Center, Two Riverside Center and Three Riverside Center.

XX.    MISCELLANEOUS.

       A.     This Amendment sets forth the entire agreement between the parties
              with respect to the matters set forth herein. There have been no
              additional oral or written representations or agreements. Under no
              circumstances shall Tenant be entitled to any Rent abatement,
              improvement allowance, leasehold improvements, or other work to
              the Three Riverside Center Premises, or any similar economic
              incentives that may have been provided Tenant in connection with
              entering into the Lease, unless specifically set forth in this
              Amendment.

       B.     Tenant shall not record this Amendment. Landlord, however, agrees
              to execute and to deliver to Tenant for recordation or
              registration, at Tenant's cost and expense, a memorandum or notice
              of this Amendment in the form attached hereto as Exhibit F-1. If
              the Lease is terminated before the Term expires, upon Landlord's
              request the parties shall execute, deliver and record an
              instrument acknowledging the above and the date of the termination
              of this Lease, and Tenant appoints Landlord its attorney-in-fact
              in its name and behalf to execute the instrument if Tenant shall
              fail to execute and deliver the instrument after Landlord's
              request therefor within 10 days.

       C.     Except as herein modified or amended, the provisions, conditions
              and terms of the Lease shall remain unchanged and in full force
              and effect.

       D.     In the case of any inconsistency between the provisions of the
              Lease and this Amendment, the provisions of this Amendment shall
              govern and control.

                                       11

<PAGE>   12


       E.     Submission of this Amendment by Landlord is not an offer to enter
              into this Amendment but rather is a solicitation for such an offer
              by Tenant. Landlord shall not be bound by this Amendment until
              Landlord has executed and delivered the same to Tenant; provided,
              that, if Landlord shall not have executed and delivered the same
              to Tenant within seven (7) business days after the same has been
              executed by Tenant and submitted to Landlord, Tenant shall have
              the right by written notice to Landlord at any time prior to the
              date on which a fully executed copy of this Amendment is delivered
              to Tenant, to declare this Amendment null and void.

       F.     The capitalized terms used in this Amendment shall have the same
              definitions as set forth in the Lease to the extent that such
              capitalized terms are defined therein and not redefined in this
              Amendment.

       G.     Tenant hereby represents to Landlord that Tenant has dealt with no
              broker in connection with this Amendment. Tenant agrees to
              indemnify and hold Landlord, its members, principals,
              beneficiaries, partners, officers, directors, employees,
              mortgagee(s) and agents, and the respective principals and members
              of any such agents (collectively, the "Landlord Related Parties")
              harmless from all claims of any brokers, including without
              limitation Roy Hirshland, Spaulding & Slye or any successor
              thereto, claiming to have represented Tenant in connection with
              this Amendment. Landlord hereby represents to Tenant that Landlord
              has dealt with no broker in connection with this Amendment.
              Landlord agrees to indemnify and hold Tenant, its members,
              principals, beneficiaries, partners, officers, directors,
              employees, and agents, and the respective principals and members
              of any such agents (collectively, the "Tenant Related Parties")
              harmless from all claims of any brokers claiming to have
              represented Landlord in connection with this Amendment.


         IN WITNESS WHEREOF, Landlord and Tenant have duly executed this
Amendment as of the day and year first above written.



WITNESS/ATTEST:                       LANDLORD:

                                      EOP-RIVERSIDE  PROJECT,  L.L.C, A DELAWARE
                                      LIMITED  LIABILITY COMPANY

                                      By: Beacon Property Management
                                          Corporation, a Delaware corporation,
                                          its managing member

/s/ Hannah Song                       By: /s/ Gregory R. Clancy
----------------------------------        -------------------------------------

Name (print):  Hannah Song            Name: Gregory R. Clancy
              --------------------          -----------------------------------

/s/ Harcie Sacehson                   Title: VICE PRESIDENT - Leasing
----------------------------------           ----------------------------------

Name (print):  Harcie Sacehson
              --------------------


WITNESS/ATTEST:                       TENANT:

                                      ALLAIRE CORPORATION, A
                                      CORPORATION ORGANIZED UNDER THE
                                      LAWS OF THE STATE OF DELAWARE

/s/ Eric J. Smith                     By: /s/ David A. Gerth
-----------------------------------       -------------------------------------

Name (print):  Eric J. Smith          Name:  David A. Gerth
              ---------------------         -----------------------------------
                                      Title: Chief Financial Officer and Vice
-----------------------------------   President of Operations and Finance
Name (print):
              ---------------------


                                       12

<PAGE>   13



                                   EXHIBIT A-5

   OUTLINE AND LOCATION OF THE FIRST FLOOR PREMISES IN THREE RIVERSIDE CENTER



       This Exhibit is attached to and made a part of the Lease dated as of , ,
2000, by and between EOP-RIVERSIDE PROJECT, L.L.C, A DELAWARE LIMITED LIABILITY
COMPANY ("Landlord") and ALLAIRE CORPORATION, A CORPORATION ORGANIZED UNDER THE
LAWS OF THE STATE OF DELAWARE ("Tenant") for space in the Building located at
275 Grove Street, Newton, MA.


                               [1ST FLOOR LAYOUT]


                                       1
<PAGE>   14



                                   EXHIBIT A-6

   OUTLINE AND LOCATION OF THE FOURTH FLOOR PREMISES IN THREE RIVERSIDE CENTER



       This Exhibit is attached to and made a part of the Lease dated as of , ,
2000, by and between EOP-RIVERSIDE PROJECT, L.L.C, A DELAWARE LIMITED LIABILITY
COMPANY ("Landlord") and ALLAIRE CORPORATION, A CORPORATION ORGANIZED UNDER THE
LAWS OF THE STATE OF DELAWARE ("Tenant") for space in the Building located at
275 Grove Street, Newton, MA.



                               [4TH FLOOR LAYOUT]


                                       2
<PAGE>   15


                                   EXHIBIT A-7

   OUTLINE AND LOCATION OF THE FIRST FLOOR PREMISES IN THREE RIVERSIDE CENTER
                          (I.E. THE UNENCUMBERED SPACE)



       This Exhibit is attached to and made a part of the Lease dated as of , ,
2000, by and between EOP-RIVERSIDE PROJECT, L.L.C, A DELAWARE LIMITED LIABILITY
COMPANY ("Landlord") and ALLAIRE CORPORATION, A CORPORATION ORGANIZED UNDER THE
LAWS OF THE STATE OF DELAWARE ("Tenant") for space in the Building located at
275 Grove Street, Newton, MA.


                                 [FLOOR LAYOUT]


                                       3
<PAGE>   16



                                   EXHIBIT B-1

                               RULES & REGULATIONS
                              FOR CONSTRUCTION WORK



The following Rules and Regulations should be incorporated into all agreements
between a tenant and contractors or vendors performing construction services on
the premises.

1.   DEFINITIONS

     1.1   Building:                     Riverside Center
                                         275 Grove Street
                                         Newton, Massachusetts

     1.2   Property Manager:             Robert Baker

     1.3   Chief Engineer:               Michael O'Shaughnessy

     1.4   TIW Project Manager:          As assigned

     1.5   Regular Business Hours:       Monday - Friday, 8:00 a.m. - 6:00 p.m.
                                         Saturday, 8:00 a.m. - 1:00 p.m.
                                         excluding holidays

     1.6   Tenant:                       The capitalize term "Tenant" shall
                                         refer to Allaire Corporation and its
                                         permitted subtenants and assignees.
                                         The non-capitalized term "tenant" shall
                                         refer to any occupant of the Building.

     1.7   Special Work:                 Any part of the Work which involves the
           operations:                   following

                                         a. All utility disruptions, shut-offs,
                                            and turnovers

                                         b. Activities involving high levels of
                                            noise, including, but not limited
                                            to, demolition, coring, drilling,
                                            and ramsetting.

                                         c. Activities resulting in excessive
                                            dust or odors, including, but not
                                            limited to, demolition and spray
                                            painting.

     1.8   Contractor or Vendor:         Any service provider contracting
                                         directly with Tenant to install
                                         furniture or equipment, or perform
                                         physical improvements to the premises.

     1.9   Tradesperson:                 Any employee (including, without
                                         limitation, any mechanic or laborer)
                                         employed by a Contractor or Vendor
                                         performing work.

2.   INSURANCE

     2.1   The Contractor shall purchase from and maintain in a company or
           companies lawfully authorized to do business in the jurisdiction in
           which the Project is located insurance for protection from claims
           under worker's or workmen's compensation acts and other employee
           benefits acts which are applicable, claims for damages because of
           bodily injury, including death, and from claims for damages, other
           than to the Work itself, to property which may arise out of or
           result from the Contractor's operations under the Contract, whether
           such operations be by the Contractor or by a Subcontractor or anyone
           directly or indirectly employed by any of them. This insurance shall
           be written for not less than limits of liability set forth herein or
           required by law, whichever



                                       4
<PAGE>   17


     coverage is greater, and shall include contractual liability insurance
     applicable to the Contractor's obligations hereunder. Certificates of such
     insurance shall be filed with the Landlord prior to the commencement of the
     Work.

2.2  The insurance required by Subparagraph 2.1 shall be written for not less
     than the following, or greater if required by law:

     1.   Workers Compensation:

          (a) State.................................................. Statutory

          (b) Applicable Federal:.................................... Statutory

          (c) Employer's Liability...................................$1,000,000

     2.   Comprehensive General Liability (including but not limited to
          comprehensive form, premises operations, explosion and collapse hazard
          and underground hazard, products and completed operations hazard,
          contractual liability, broad form property damage (including completed
          operations), independent contractors' protective, personal injury,
          automobile liability comprehensive form for owned, hired and non-owned
          vehicles):

          (a)  Combined single limits for bodily and property damages:

               $5,000,000 ..................................  Each Occurrence

               $5,000,000 .................................. Annual Aggregate

     (b)  Products and Completed Operations to be maintained for 3 years after
          final payment.

          (b)  Property Damage Liability Insurance shall provide X, C and U
               coverage if Contractor's operations involve any exposure to
               explosion, collapse or underground damage.



                                       5

<PAGE>   18


     2.3  The certificates of insurance shall contain the following provisions:

               1.   Name the Landlord, Landlord's agents, beneficiaries and
                    mortgagee, and Architect as additional insured (excluding
                    workers' compensation), including EOP-RIVERSIDE PROJECT,
                    L.L.C., BEACON PROPERTY MANAGEMENT CORPORATION, AND EQUITY
                    OFFICE PROPERTIES TRUST;

               2.   In the event of any change in the limits of liability,
                    decrease in coverage or other material change in coverage,
                    or the cancellation of insurance in its entirety, the
                    insurer must give Landlord, Landlord's agents, beneficiaries
                    mortgagee, and Architect written notice at least thirty (30)
                    days prior to the effective date of such change or
                    cancellations, and insurance coverage shall remain in force
                    during said thirty (30) day period; and

               3.   Waiver of any right of subrogation of the insurers against
                    Landlord, Landlord's agents, beneficiaries an mortgagee, and
                    the Architect.

     2.4  At Landlord's request, Contractor shall cause any bank and/or
          financial institution and/or any trustee designated by Landlord to be
          added as additional insureds under the insurance policies required by
          Subparagraph 2.1.

     2.5  If Contractor fails to carry or provide evidence of insurance provided
          for herein, Landlord may, but shall not be obligated to, procure the
          same and charge the cost thereof to Contractor.

     2.6  Contractor shall carry sufficient comprehensive insurance on its
          equipment at the site an on route to or from the site as may be
          necessary to fully protect itself, and Contractor acknowledge that
          Landlord shall have no responsibility or liability therefor.

     2.7  Contractor shall certify to the Landlord that it has obtained or will
          obtain similar certificates of insurance form each of its
          Subcontractor before their work commences. Each subcontractor must be
          covered by insurance of the same character and in the same amounts as
          the Contractor unless the Contractor and the Landlord agree that a
          reduced coverage is adequate. Each Subcontractor's insurance shall
          cover the Landlord's agents and beneficiaries and the Architect.

3. SCHEDULING

     3.1  COORDINATION

           a.   All Work to be carried out expeditiously and with minimum
                disturbance and disruption to the operation of the Building and
                without causing discomfort, inconvenience, or annoyance to any
                of the other tenants or occupants of the Building or the public
                at large.

          b.   All schedules for the performance of construction, including
               delivery of materials, shall be coordinated through the TIW
               Project Manager and the Property Manager. The TIW Project Manager
               reserves the right, without incurring any liability to Tenant,
               Contractor, or Vendor, to stop activities and/or require
               rescheduling of Tenant Work based upon adverse impact on tenants
               or occupants of the Building, Landlord's or another party's
               performance of work in the Building, including any base building
               work or tenant work, or on the maintenance or operation of the
               Building.

          c.   If any Work requires the shutdown of risers and mains for
               electrical, mechanical, life-safety, or plumbing systems, such
               work to be approved by and coordinated with the Chief Engineer,
               and at the discretion of the Chief Engineer, to be supervised by
               the Chief Engineer or designated representative. The Contractor
               or Vendor is responsible for protecting all existing systems and
               equipment as required.

          d.   Contractor to notify all local regulatory authorities of all
               shutdowns of electrical, mechanical, life safety, or plumbing
               systems, as required.


                                       6

<PAGE>   19


     3.2   TIME RESTRICTIONS

           a.   Subject to Paragraph 2.1 of these Rules and Regulations, prior
                to the date on which any portion of the Building is occupied by
                tenants or other occupants, general construction work will be
                permitted at all times, including during Regular Business Hours.
                From and after the date on which any portion of the Building is
                occupied by tenants or other occupants, Property Manager shall
                have the right to restrict the hours in which construction work
                may be performed in order to minimize any disruption to the
                business activities of such tenants or occupants. Without
                limitation, Property Manager shall have the right to require
                construction work to be performed only at times outside Regular
                Business Hours.

           b.   Contractor or Vendor to provide Property Manager with at least
                twenty-four (24) hours notice to schedule Special Work. From and
                after the date on which any portion of the Building is occupied
                by tenants or other occupants, such Special Work will be
                permitted only during periods outside of Regular Business Hours
                as agreed to by the Property Manager.

           c.   The delivery of construction materials to the Building,
                distribution within the Building, and the removal of waste
                materials will, from and after the date on which any portion of
                the Building is occupied by tenants or other occupants, be
                confined to periods outside Regular Business Hours, unless
                otherwise specifically permitted in writing by the TIW Project
                Manager.

           d.   If coordination, labor disputes, or other circumstances require,
                the Property Manager may change the hours during which regular
                construction work can be performed and/or restrict or refuse
                entry to the Building by any Contractor or Vendor.

4.   CONTRACTOR OR VENDOR PERSONNEL

     4.1   CONDUCT

           a.   While in or about the Building, all Contractors and Vendors must
                perform in a dignified, quiet, courteous, and professional
                manner at all times. Tradespersons must wear clothing suitable
                for their work and shall remain fully attired at all times. Each
                Contractor and Vendor will be responsible for his/her
                Tradesperson's behavior and conduct.

           b.   The TIW Project Manager reserves the right to prohibit any
                Contractor, Vendor, or Tradesperson from working on the premises
                for disturbing any tenant, occupant, contractor, vendor, or
                tradesperson, interfering with the work of others, or in any way
                displaying conduct or performance not compatible with the
                Owner's standards.

     4.2   ACCESS

           a.   Contractors and Vendors must contact the TIW Project Manager to
                coordinate Building access. Elevators will not be available for
                any purpose in connection with the performance of work by
                Contractor in the Building, including, without limitation, for
                the purpose of transporting any persons to or from the premises
                in which work will be performed. Access to the Building before
                and after Regular Business Hours, all day on weekends and
                holidays, or any other hours designated from time to time by the
                TIW Project Manager, will only be provided following receipt of
                twenty-four (24) hours advanced notice by the TIW Project
                Manager and Chief Engineer.

           b.   Contractors and Vendors must obtain permission from the TIW
                Project Manager prior to undertaking work in any space outside
                the Contractor's Work limits. This requirement specifically
                includes ceiling spaces below the premises where any work
                required must be undertaken at the convenience of the affected
                tenant and outside of Regular Business Hours. Contractor or
                Vendor undertaking such work shall ensure that all work,
                including work required to reinstate removed items and cleaning,
                be completed prior to opening of the next business day.


                                       7

<PAGE>   20

           c.   No Contractor or Vendor will be permitted to enter any private
                or public space in the Building, other than the common areas of
                the Building necessary for direct access to the area of Work for
                which he/she has been employed, without the prior approval of
                the TIW Project Manager.

           d.   Contractor or Vendor will ensure that all furniture, equipment,
                and accessories in areas potentially affected by the Work are
                adequately protected by means of drop cloths or other
                appropriate measures. In addition, Contractor and Vendor shall
                be responsible for maintaining security to the extent required
                by the Property Manager.

           e.   Temporary access doors for tenant construction areas connecting
                with a public corridor will consist of building standard door,
                frame, hardware, and lockset. A copy of the key will be
                furnished to the Property Manager.

           f.   Unless otherwise agreed to by Property Manager, bulk loading of
                material to be made via lift or crane through a removed window.
                Contractor or Vendor to protect all existing construction as
                required.

     4.3   SAFETY

           a.   Contractor or Vendor to police ongoing construction operations
                and activities at all times, keeping the premises orderly,
                maintaining cleanliness in and about the premises, and ensuring
                safety and protection of all areas, including truck docks,
                elevators, lobbies, and all other public areas which are used
                for access to the premises.

           b.   Contractor or Vendor to appoint a supervisor who will be
                responsible for all safety measures, as well as for compliance
                with all applicable governmental laws, ordinances, rules and
                regulations such as, for example, "OSHA" and "Right-to-Know"
                legislation.

           c.   Contractor or Vendor to take all reasonable precautions to
                prevent damage to property, both visible and concealed, and will
                restore the Building to substantially the same condition
                existing prior to the Contractor's or vendor's entry, to the
                satisfaction of the TIW Project Manager. While performing
                services hereunder, the Contractor or Vendor will immediately
                notify the TIW Project Manager of any defective condition in the
                Building of which he/she becomes aware. Any damage caused by
                Tradespersons will be the responsibility of the Contractor or
                Vendor. Costs for Owner's repair of such damage will be charged
                directly to the Tenant.

           d.   Contractor or Vendor to maintain proper emergency egress for the
                area of Work and adjacent areas of the Building during all
                phases of the Work.

           e.   Contractor or Vendor to notify the TIW Project Manager if any of
                its employees, equipment, or motor vehicles or that of any
                subcontractors are involved in an accident or injury while on
                the Property within twenty four (24) hours. Contractor of Vendor
                to provide a detailed accident report within three (3) business
                days.

     4.4   PARKING

           a.   Parking is not allowed in or near truck docks, in accessible
                parking spaces or loading zones, fire access lanes, or private
                ways in or surrounding the property. Vehicles so parked will be
                towed at the expense of the Contractor or Vendor for whom the
                owner of such vehicle is employed.

           b.   The availability of parking in any parking areas of the Building
                is limited. Use of such parking for Contractor or Vendor and
                his/her personnel is restricted and must be arranged with and
                approved by the TIW Project Manager.

           c.   In no event may any office and/or storage trailers be parked at
                the Building or at the property on which the Building is
                located.

5.   BUILDING MATERIALS

     5.1   DELIVERY


                                       8

<PAGE>   21


           All deliveries of construction materials to be made at the
           predetermined times coordinated with and approved by the TIW Project
           Manager, and to be carried out safely and expeditiously only at the
           location determined by the TIW Project Manager. Contractor shall work
           together in good faith with any other contractors performing work at
           the Building to assure that materials can be delivered to the
           Building and respective premises with minimal disruption. In addition
           to being entitled to designate and coordinate the times for material
           deliveries, the TIW Project Manager and/or Property Manager may act
           as the sole arbitrator for the purpose of resolving any disputes in
           connection with any such activities.

     5.2   TRANSPORTATION IN BUILDING

           a.   Distribution of materials from delivery point to the work area
                in the Building to be accomplished with the least disruption to
                the operation of the Building possible. Subject to the terms of
                Section 4.2.f., the Property Manager may designate elevators for
                material delivery.

           b.   Contractor or Vendor will provide adequate protection for all
                carpets, wall surfaces, doors and trim in all public areas
                through which materials are transported. Contractor or Vendor
                must continuously clean all such areas. Protective measures
                shall include runners over carpet, padding in elevators, and any
                other measures determined by the TIW Project Manager and
                Property Manager.

           c.   Any damage caused to the building through the movement of
                construction materials or otherwise will be the responsibility
                of the Contractor or Vendor. Costs for Owner's repair of such
                damage will be charged directly to the Tenant.

     5.3   STORAGE AND PLACEMENT

           a.   All construction materials to be stored only in the premises
                where they are to be installed. No storage or staging of
                materials will be permitted in public areas, loading docks,
                corridors leading to the premises or any other portion of the
                Building or Property other than the premises in which such
                materials will be installed.

           b.   No flammable, toxic, or otherwise hazardous materials may be
                brought in or about the Building unless: (I) authorized by the
                Chief Engineer, (ii) all applicable laws, ordinances, rules, and
                regulations are complied with, and (iii) all necessary permits
                have been obtained. All necessary precautions will be taken by
                the Contractor or Vendor when handling such materials so to
                avoid damage or injury.

     5.4   SALVAGE AND WASTE REMOVAL

           a.   All rubbish, waste, and debris will be neatly and cleanly
                removed from the Building daily by the Contractor or Vendor
                unless otherwise approved by TIW Project Manager. The Building's
                trash compactor will not be used for construction or debris. For
                any demolition and debris, Contractor, at its sole cost and
                expense, must make arrangements with the Property Manager for
                scheduling and location of an additional dumpster to be supplied
                by Contractor. Where, in the opinion of the TIW Project Manager,
                such arrangements are not practical, Contractor will make
                alternative arrangements for rubbish removal. Contractor shall
                not be entitled to install more than one trash chute to dispose
                of rubbish, waste and debris in connection with the Work.

           b.   Toxic or flammable waste is to be properly removed daily and
                disposed of in full accordance with all applicable laws,
                ordinances, rules, and regulations.

         c. Contractor or Vendor will, prior to removing any item (including,
         without limitation, building standard doors, frames and hardware, light
         fixtures, ceiling diffusers, ceiling exhaust fans, sprinkler heads,
         fire horns, ceiling speakers, and smoke detectors) from the Building,
         notify the TIW Project Manager that he/she intends to remove such item.
         At the election of TIW Project Manager, Contractor or Vendor to deliver
         any such items, at no cost, to an area designated by the TIW Project
         Manager to an area within the Building or complex in which the Building
         is located.


                                       9

<PAGE>   22

         d. Contractor shall be responsible for obtaining its own Port-a-John or
         other sanitary facilities for use by Tradespersons, the location of
         which shall be subject to approval of the Property Manager. Contractor
         shall be responsible for having the sanitary facilities cleared at
         regular intervals and for removing such sanitary facilities from the
         Building and property upon the completion of the work. In no event
         shall Contractor or Tradespersons be entitled to use the Building
         restrooms or the sanitary facilities or any other contractor.

6.       MISCELLANEOUS.

           a.   All transformers, chillers, air conditioners,
                mechanical/ventilation systems, HVAC equipment, and similar
                devices shall be designed, located and baffled using
                appropriate. Acoustical screening to minimize the noise
                produced. The noise produced by this equipment shall comply with
                the City of Newton Noise Ordinance and shall not exceed 51 dBa
                during the day and 46 dBa during the night as measured at the
                property line or any location on immediately abutting
                residential properties. Emergency generators will be designed to
                meet City of Newton noise regulations. Any such equipment must
                be retested from time to time to confirm that it will continue
                to comply with such standards.

           b.   No Contractors or Tradesmen shall park on neighborhood streets.

           c.   Noise levels shall comply with the City's Noise Control
                Ordinance, Section 20-13.

           d.   Trucks shall only access the site to and from Route 128, except
                when the MBTA bridge is too low to allow passage of large
                equipment, in which case, the routes and times shall be reviewed
                and approved by the Police Department.

           d.   Noise from heaters used during construction in winter conditions
                shall comply with the City's Noise Control Ordinance.




                                       10
<PAGE>   23


                                   EXHIBIT B-2

                       INDOOR AIR QUALITY (IAQ) GUIDELINES
                              FOR CONSTRUCTION WORK


The following Indoor Air Quality Guidelines are herewith incorporated into all
agreements with Contractors and Vendors performing construction services on the
premises.

1.   MATERIALS

     The Contractor shall use only application-approved materials with the
     lowest content by volume of toxic or irritating chemicals. New carpet must
     have a green label certified by the Carpet and Rug Institute (CRI) and be
     installed according to CRI installation guidelines. Contractor shall avoid
     materials containing chemicals listed as potentially carcinogenic,
     mutagenic, teratogenic, neurotoxic, or "sensitizing." The following
     materials are banned from new installations:

     a.   Materials containing greater than trace (0.1%) amounts of asbestos.

     b.   Materials containing any halogenated hydrocarbon solvents (e.g.
          methylene chloride, tetrachloroethylene, trichloroethylene,
          trichloroethane).

     c.   HVAC components internally lined with permeable man-made mineral fiber
          products unless coated with "Tuffcoat" or other tough, resilient
          coating or mat surface that provides a smooth, non-shedding surface in
          contact with the air stream.

2.   SUBMITTALS & INFORMATION

     2.1  Prior to starting work, the Contractor shall furnish information
          copies of MSDS forms to the TIW Project Manager for all materials to
          be installed and utilized during installation.

     2.2  The Contractor will assist the TIW Project Manager in providing
          pre-construction information and/or information sessions to the Tenant
          during project planning stages and/or at least twenty-four (24) hours
          prior to project initiation. The information and/or information
          sessions shall address the following:

          a.   Project scope and duration.

          b.   Anticipated construction impacts on indoor air quality (IAQ) and
               workplace conditions.

          c.   Methods to minimize impact (e.g. engineering controls, material
               selection).

          d.   Methods to record, investigate, and resolve occupant complaints
               related to construction impacts on IAQ or workplace conditions.

3.   METHODS

     3.1  General

          a.   The Contractor shall maintain work area clean and free of open
               containers of paint, cleaners, chemicals, loose trash and
               garbage. All flammable and hazardous substances shall be stored
               to prevent spillage and in accordance with National Fire
               Protection Association (NFPA) codes and OSHA regulations. When
               possible, flammable and hazardous materials shall be removed from
               the Building on a daily basis. Otherwise, appropriate storage
               arrangements shall be made with the Chief Engineer.

          b.   No methods to isolate the Work area, contain odors and
               contaminants, or ventilate odors and contaminants shall impede
               emergency egress from the area of work or any area of the
               Building.

                                       11

<PAGE>   24

          c.   No equipment powered by a combustion engine will be permitted in
               the premises.

          d.   When possible, the Contractor shall use application methods that
               generate the least amount of airborne contaminants (e.g. brush
               vs. spray application of paint).

          e.   Unless approved by product specifications, the Contractor shall
               not install wet or water-damaged building materials. The
               Contractor shall protect stored materials from water and moisture
               prior to installation. The Contractor shall protect new building
               assemblies from water damage following installation and inspect
               for signs of ineffective water and moisture control (e.g.
               condensation on pipes and ducts and roof and drain leaks)
               following installation.

     3.2  Isolation of Work Area

          a.   Where feasible, construction site passageways abutting tenant
               occupied locations shall incorporate single chamber "air locks"
               (two sets of doors or plastic strip doors at opposite ends of an
               enclosed chamber or small room) into each construction site
               entrance. Plastic strip doors shall be of minimum 0.120" thick
               material with full overlap. Once installed, the air lock shall
               remain in place for the duration of the project or until such a
               time as its presence blocks final completion of the renovations.
               The Contractor's passage routes should avoid or minimal intersect
               tenant occupied areas of the building.

               The Contractor shall submit plan indicating construction site
               passageways for approval to the TIW Project Manager and shall
               construct and use only these passageways for access to the area
               of work

          b.   All persons and materials passing to the construction site should
               be fully in the air lock and the door to the tenant occupied area
               closed before opening the construction site door (or flaps). At
               least one (set of) air lock door(s) (or flaps) must remain closed
               throughout the renovation process. All persons leaving the site
               shall clean their feet on a floor mat in the air lock prior to
               entering the tenant occupied part of the building. The Contractor
               shall clean the floor mat regularly.

     3.2  Containment & Ventilation of Odors & Contaminants

          a.   Upon mobilization, the Contractor and the HVAC subcontractor
               shall meet with the Chief Engineer to review the building HVAC
               system.

          b.   The Contractor shall submit for approval to the Building Engineer
               proposed plan to contain and ventilate odors and contaminants.

          c.   The Contractor is responsible for ensuring that odors and
               contaminants are contained. Activities that have potential to
               emit airborne contaminants must be coordinated with the TIW
               Project Manager. The Contractor shall:

               i.   Isolate all return air pathways from the construction area.

               ii.  Cut and cap all supply air ducts serving the construction
                    area except for temporary ducts supplying air to the
                    construction area for temporary heat and air conditioning.

               iii. Monitor and maintain construction site at negative pressure
                    at least (-0.02" w.c.) relative to tenant occupied spaces by
                    installing and operating temporary exhaust to outdoors
                    through existing building exhaust systems or through
                    temporary louvers installed in place of windows or exterior
                    doors. Preparation should be made to replace designated
                    windows or doors with appropriate weatherproof exhaust
                    equipment manifolds. Upon completion of construction, the
                    Contractor shall restore all repositioned windows and doors
                    to original condition and location.

               iv.  Where renovation site lacks access to perimeter windows,
                    doorways, or existing building exhaust systems, "negative
                    air machines" with HEPA


                                       12

<PAGE>   25


                    and/or activated-carbon filters may be utilized to
                    re-circulate air to the building, preferably to unoccupied
                    building locations.

               v.   Install and maintain air-tight seals at all openings between
                    tenant occupied areas of the building and the construction
                    site (e.g. doorways, corridors, air plenums, chases, open
                    conduits and duct work) throughout the course of
                    construction activities. Upon completion of construction,
                    the Contractor shall remove all installed barriers and
                    seals.

               vi.  The Contractor shall ensure that the rest of the building
                    outside the project area remains unaffected by the project.
                    In particular, all HVAC systems altered for the purposes of
                    controlling site contaminants must continue to provide at
                    least the minimum outside air ventilation rate required by
                    all applicable codes at the time the facility was
                    constructed, to all occupied spaces.

4.   COMPLETION OF WORK

     4.1  Upon completion of Work, the Contractor shall clean all air plenums
          and mechanical system components determined to have deteriorated as a
          result of the the Contractor's work. All air filters shall be changed.

     4.2  The area of work should be ventilated and exhausted for a period of a
          minimum of 48-72 hours prior to occupancy by Tenant to allow newly
          installed building materials, finishes, and office equipment to
          off-gas volatile organic compounds, if any.

     4.3  Contractor shall verify that all mechanical systems are balanced and
          working properly and shall provide balancing reports to the Chief
          Engineer.


                                       13

<PAGE>   26

                                   EXHIBIT F-1

                          AMENDMENT TO NOTICE OF LEASE


     This Amendment to Notice of Lease between EOP-RIVERSIDE PROJECT, L.L.C, A
DELAWARE LIMITED LIABILITY COMPANY, as Landlord, and ALLAIRE CORPORATION, A
CORPORATION ORGANIZED UNDER THE LAWS OF THE STATE OF DELAWARE, as Tenant, is
hereby given pursuant to the provisions of Chapter 183, Section 4 of the
Massachusetts General Laws.

     WHEREAS, Landlord and Tenant are parties to that certain Lease dated
November 23, 1999 with respect to the 270,446 square feet of space located in
the buildings known as One Riverside Center and Two Riverside Center, 275 Grove
Street, Newton, Middlesex County, Massachusetts, a notice of which is recorded
with the Middlesex (South) Registry of Deeds in BOOK ____, PAGE ____ (the
"Notice of Lease").

     WHEREAS, Landlord and Tenant have entered into a First Amendment of even
date herewith whereby Tenant has leased from Landlord and Landlord has leased to
Tenant upon the terms and conditions set forth therein and in the Lease, an
additional 78,014 square feet of space located in the building known as Three
Riverside Center, 275 Grove Street, Newton, Middlesex County, Massachusetts.

     NOW, THEREFORE, Landlord and Tenant hereby agree to amend the Notice of
Lease as follows:

1.   The "Description of the Premises" appearing in the Notice of Lease is
hereby deleted in its entirety and replaced with the following:


     "Description of Premises:

     Approximately 348,460 square feet of space on the 1st, 2nd and 3rd floors
     of the building commonly known as One Riverside Center, the 1st and 2nd
     floors of the building commonly known as Two Riverside Center and the 1st
     and 4th floors of the building commonly known as Three Riverside Center
     ("Premises") shown on the sketch plan attached hereto as Exhibit "A" and
     located at 275 Grove Street, Newton, MA (the "Property") more particularly
     described on Exhibit "B" attached hereto and made a part hereof."

2.   Except as modified herein, the Notice of Lease remains unchanged and is in
full force and effect.


                                       14

<PAGE>   27


     WITNESS the execution hereof as a sealed instrument as of the 31st day of
May, 2000.

WITNESS/ATTEST:                         LANDLORD:

                                        EOP-RIVERSIDE PROJECT, L.L.C, A
                                        DELAWARE LIMITED LIABILITY COMPANY

                                        By: Beacon Property Management
                                            Corporation, a Delaware corporation,
                                            its managing member

/s/ Hannah Song                             By: /s/ Gregory R. Clancy
--------------------------------                --------------------------------

Name (print): Hannah Song                   Name: Gregory R. Clancy
              ------------------                  ------------------------------

/s/ Marcie T. Jacobson                      Title: VICE PRESIDENT - Leasing
--------------------------------                  ------------------------------

Name (print): Marcie T. Jacobson
             -------------------


WITNESS/ATTEST:                         TENANT:

                                        ALLAIRE CORPORATION, A
                                        CORPORATION ORGANIZED UNDER THE
                                        LAWS OF THE STATE OF DELAWARE

                                        By: /s/ David A. Gerth
---------------------------------           ------------------------------------

Name (print):                           Name:  David A. Gerth
             ---------------------

----------------------------------      Title: Chief Financial Officer and Vice
                                        President of Operations and Finance
Name (print):
             ---------------------


                                       15

<PAGE>   28


                             STATE OF MASSACHUSETTS

                     , ss                                      May 31, 2000
[County]

     Then personally appeared the above-named Gregory Clancy, the VP of Beacon
Property Management Corporation, a Delaware corporation, the managing member of
EOP-Riverside Project, L.L.C., a Delaware limited liability company, known to me
to be the person described in and who executed the foregoing instrument and
acknowledged the same to be his free act and deed and that of said Beacon
Property Management Corporation as the managing member of EOP-Riverside Project,
L.L.C., before me,

                                       /s/ Kimberly C. Ruby
                                       ----------------------------------------
                                       Notary Public
                                       My Commission Expires: September 8, 2006


                          COMMONWEALTH OF MASSACHUSETTS

Middlesex            , ss                                        5/11/00
[County]

     Then personally appeared the above-named David A. Gerth, the Chief
Financial Officer and Vice President for Operations and Finance of Allaire
Corporation, a Delaware corporation, known to me to be the person described in
and who executed the foregoing instrument and acknowledged the same to be his
free act and deed and that of said Allaire Corporation, before me,


                                       /s/ Victoria Sullivan Reiff
                                       ----------------------------------------
                                       Notary Public
                                       My Commission Expires: 2005



                                       16