<PAGE>

                                  EXHIBIT 10.9

                              400 Technology Square
                                Building No. 565
                         Cambridge, Massachusetts 02139

                                 FIFTH AMENDMENT
                      Execution Date: As of January 1, 2005

      LANDLORD:          Technology Square Finance, LLC, a Massachusetts limited
                         liability company, successor in interest to Technology
                         Square LLC

      TENANT:            Forrester Research, Inc.

      EXISTING
      PREMISES:          Areas on Floors 2-8 of the Building, containing
                         approximately 145,551 rentable square feet of office
                         space, substantially as shown on Lease Plan, Exhibit 2,
                         Sheets 1 through 7, attached to the Lease; and
                         approximately 1,846 rentable square feet of storage
                         space on Floor 10 ("Storage Premises"), substantially
                         as shown on Lease Plan, Exhibit A, attached to the
                         Second Amendment, dated February 8, 2001

      LEASE
      EXECUTION
      DATE:              May 6, 1999

      TERMINATION
      DATE:              September 30, 2006

      PREVIOUS
      LEASE
      AMENDMENTS:        First Amendment dated as of September 9, 1999 Second
                         Amendment dated February 8, 2001 Third Amendment to
                         Lease dated December 13, 2002 Fourth Amendment to Lease
                         dated December 22, 2003

      EXTENDED
      TERMINATION
      DATE:              September 30, 2011

      DELETED
      PREMISES:          Floor 8, containing 20,793 rentable square feet

                                      -1-
<PAGE>

      REMAINDER
      PREMISES:          The Existing Premises, less the Deleted Premises,
                         containing 124,758 rentable square feet, as shown on
                         Lease Plan, Exhibit 2, Sheets 1 through 6, attached to
                         the Lease; and the Storage Premises

      WHEREAS, Tenant desires to extend the term of the lease for an additional
term;

      WHEREAS, Landlord is willing to extend the term of the lease for an
additional term upon the terms and conditions hereinafter set forth;

      NOW THEREFORE, the parties hereby agree that the above-referenced lease,
as previously amended (the "Lease"), is hereby further amended as follows:

      1. TERMINATION OF LEASE IN RESPECT OF DELETED PREMISES

      The term of the Lease in respect of the Deleted Premises is hereby
terminated effective as of December 31, 2004 ("Deleted Premises Termination
Date"). The parties hereby acknowledge that Tenant has vacated the Deleted
Premises and has delivered the Deleted Premises to Landlord in the condition in
which Tenant is required, pursuant to the Lease (including, without limitation,
Article 22 thereof) to deliver the Premises at the expiration or prior
termination of the term of the Lease. Novartis Institute for Biomedical
Research, Inc. ("Novartis") currently occupies the Deleted Premises under and
pursuant to a certain Sublease from Tenant dated as of November 22, 2002 (the
"Sublease"). Landlord hereby represents and warrants to Tenant that Landlord has
entered into a direct lease of the Deleted Premises to Novartis. Accordingly,
this Amendment is entered into in anticipation of Novartis and Tenant entering
into an agreement in form and substance satisfactory to Tenant simultaneously
with the execution and delivery of this Amendment by which the Sublease is
terminated as of the Deleted Premises Termination Date with the same effect as
if the Deleted Premises Termination Date were the Expiration Date thereunder.

      From and after January 1, 2005, any reference in the Lease to the
"Premises" shall refer to the Remainder Premises described above.

      2. EXTENSION OF TERM OF LEASE IN RESPECT OF REMAINDER PREMISES

      The term of the Lease is hereby extended for an additional term
("Additional Term") commencing as of October 1, 2006, and terminating as of
September 30, 2011 ("Extended Termination Date "). Any reference in the Lease or
this Amendment to the initial term of the Lease shall refer to such term as
extended for the Additional Term. Said Additional Term shall be upon all of the
same terms and conditions of the Lease in effect immediately preceding the
commencement of such Additional Term (including, without limitation, Tenant's
obligation to pay for electricity, pursuant to Article 8.1 of the Lease), except
as follows:

                                      -2-
<PAGE>

      A. The Yearly Rent during the Additional Term shall be as follows:

<TABLE>
<CAPTION>
    Time Period       Yearly Rent      Yearly Rent per Square Foot      Monthly Payment
-------------------  -------------     ---------------------------      ---------------
<S>                  <C>               <C>                              <C>
October 1, 2006 -    $-0-                         $-0-                    $-0-
November 30, 2006:
December 1, 2006 -   $3,617,982.00                $29.00                  $301,498.50
December 31, 2007:
January 1, 2008 -    $3,805,119.00                $30.50                  $317,093.25
December 31, 2009:
January 1, 2010 -    $3,929,877.00                $31.50                  $327,489.75
September 30, 2011:
</TABLE>

      B. The Yearly Rent in respect of the Second Amendment Storage Premises
during the Additional Term shall be Thirty-Six Thousand Nine Hundred Twenty and
04/10 ($36,920.04) per annum (i.e., a monthly payment of $3,076.67).

      C. The Building Operating Cost Base during the Additional Term shall be
the Building Operating Costs for calendar year 2005, adjusted to reflect 95%
occupancy for a full Operating Year. The words "adjusted to reflect 95%
occupancy for a full Operating Year," shall mean for the Base Year (calendar
year 2005) that if the average annual occupancy of the Building for such
Operating Year was not at least 95%, Building Operating Costs for such Operating
Year (i.e., the Base Year) shall be "grossed up" in accordance with industry
standards and generally accepted accounting principles, consistently applied, to
what they would have been had the average annual occupancy of the Building been
95% for such Operating Year. The words "adjusted to reflect 95% occupancy for a
full Operating Year," wherever they appear elsewhere in this Fifth Amendment or
elsewhere in the Lease shall mean, as to any Operating Year other than the Base
Year, that if the average annual occupancy of the Building for such Operating
Year was not at least as high as during the Base Year, Building Operating Costs
for such Operating Year (i.e., each calendar year after the Base Year) shall be
so adjusted to what they would have been had the average annual occupancy of the
Building for such year been the higher of 95% or such average annual occupancy
during the Base Year. Such "gross-up" adjustments shall be made by increasing
those costs includable in Building Operating Costs which, according to industry
practice but depending on the specific situation of the Building, will vary
based upon the level of occupancy at the Building.

      D. The Complex Operating Cost Base during the Additional Term shall be the
Complex Operating Costs for calendar year 2005, adjusted to reflect 95%
occupancy for a full Operating Year.

      E. The Building Tax Base during the Additional Term shall be the actual
amount of Building Taxes for fiscal/tax year 2005 (i.e., July 1, 2004 - June 30,
2005).

                                      -3-
<PAGE>

      F. Tenant's Building Operating Cost Percentage during the Additional Term
shall be 64.05% (i.e., 124,758 square feet divided by the Total Rentable Area of
the Building, which is 194,776 square feet).

      G. Tenant's Complex Operating Costs Percentage during the Additional Term
shall be 10.98% (i.e., 124,758 square feet divided by the Total Rentable Area of
the Complex, which is 1,136,734 square feet).

      H. Tenant's Building Tax Percentage during the Additional Term shall be
64.05% (i.e., 124,758 square feet divided by the Total Rentable Area of the
Building, which is 194,776 square feet).

      I. In the event that any of the provisions of the Lease are inconsistent
with this Amendment or the state of facts contemplated hereby, the provisions of
this Amendment shall control.

      J. Landlord and Tenant shall, promptly after the Building Operating Cost
Base and the Complex Operating Cost Base have been determined for calendar year
2005, without waiver by Tenant of any audit rights applicable thereto, cooperate
to prepare a replacement Exhibit 16A to the Fourth Amendment to Lease, to be
used thereafter in implementing Article 9.1(b) as amended by said Fourth
Amendment. The replacement Exhibit 16A shall merely document the amounts of the
line item costs included in the Building Operating Cost Base and the Complex
Operating Cost Base and shall not, except as Landlord and Tenant may otherwise
agree in writing, add or delete any line items of cost or otherwise change the
method by which Building Operating Costs or Complex Operating Costs are
determined. The reference in said Article 9.1(b) to "2003" shall thereafter be
deemed to be to "2005."

      K. Landlord represents and warrants that the Total Rentable Area of the
Premises, the Building and the Complex as stated in this Fifth Amendment have
been determined in accordance with Exhibit 11 (Measurement Standards) attached
to the Lease, except only that laboratory exhaust shaft areas have been included
in determining the usable area of tenant premises and mechanical rooms and
penthouse areas have been included as part of each building's common area, which
exceptions do not affect the calculation of the Total Rentable Area of the
Premises or the Building, but only that of certain other laboratory buildings in
the Complex, resulting in a larger Total Rentable Area for the Complex than
would otherwise obtain through the application of Exhibit 11.

      3.    REVISED YEARLY RENT, BUILDING OPERATING COST BASE, COMPLEX OPERATING
            COST BASE AND BUILDING TAX BASE FOR THE REMAINDER OF ORIGINAL TERM

      In consideration of Tenant agreeing to an early extension of the term of
the Lease, commencing as of January 1, 2005, and ending as of September 30,
2006, the schedule of Yearly Rent, as set forth in Exhibit 1 to the Lease, shall
be revised as follows:

                                      -4-
<PAGE>

      A. Commencing as of January 1, 2005, and ending as of September 30, 2006,
Yearly Rent shall be revised as follows:

                                             Yearly Rent per
    Time Period           Yearly Rent          Square Foot      Monthly Payment
-------------------      -------------       ---------------    ---------------
January 1, 2005 -
September 30, 2006:      $3,617,982.00          $29.00            $301,498.50

      Yearly Rent for the period commencing as of January 1, 2005, and expiring
      as of September 30, 2006, is based on 124,758 rentable square feet of the
      Premises only, the parties hereby acknowledging that Tenant has no
      obligation to pay Yearly Rent in respect of 20,793 rentable square feet on
      floor 8 of the Building.

      B. Commencing as of January 1, 2005, and ending as of September 30, 2006,
the Building Operating Cost Base shall be the Building Operating Costs for
calendar year 2005, adjusted to reflect 95% occupancy for a full Operating Year.

      C. Commencing as of January 1, 2005, and ending as of September 30, 2006,
the Complex Operating Cost Base shall be the Complex Operating Costs for
calendar year 2005, adjusted to reflect 95% occupancy for a full Operating Year.

      D. Commencing as of January 1, 2005, and ending as of September 30, 2006,
the Building Tax Base shall be the actual amount of Building Taxes for
fiscal/tax year 2005 (i.e., July 1, 2004 - June 30, 2005).

      E. Commencing as of January 1, 2005, and ending as of September 30, 2006,
Tenant's Building Operating Cost Percentage shall be 64.05% (i.e., 124,758
square feet divided by the Total Rentable Area of the Building, which is 194,776
square feet).

      F. Commencing as of January 1, 2005, and ending as of September 30, 2006,
Tenant's Complex Operating Costs Percentage shall be 10.98% (i.e., 124,758
square feet divided by the Total Rentable Area of the Complex, which is
1,136,734 square feet).

      G. Commencing as of January 1, 2005, and ending as of September 30, 2006,
Tenant's Building Tax Percentage shall be 64.05% (i.e., 124,758 square feet
divided by the Total Rentable Area of the Building, which is 194,776 square
feet).

      4. LANDLORD'S CONTRIBUTION

      A. Landlord shall, in the manner hereinafter set forth, contribute up to
Six Hundred Twenty-Three Thousand Seven Hundred Ninety and 00/100 ($623,790.00)
Dollars (i.e., $5.00 per rentable square foot of floor area in the Remainder
Premises) ("Landlord's Contribution") towards the cost of leasehold improvements
to be installed by Tenant in the Remainder Premises ("Tenant's Work"). Tenant's
Work shall be performed in accordance with the Lease (including, without
limitation, Articles 12 and 13 thereof).

                                      -5-
<PAGE>

      B. Provided that Tenant is not in default of its obligations under the
Lease at the time that Tenant requests any requisition on account of Landlord's
Contribution, Landlord shall pay the cost of the work shown on each requisition
(as hereinafter defined) submitted by Tenant to Landlord within thirty (30) days
of submission thereof by Tenant to Landlord. For the purposes hereof, a
"requisition" shall mean written documentation showing in reasonable detail the
costs of the improvements then installed by Tenant in the premises. Tenant shall
submit requisition(s) no more often than monthly.

      C. Notwithstanding anything to the contrary herein contained:

      (i) Landlord shall have no obligation to advance funds on account of
Landlord's Contribution unless and until Landlord has received the requisition
in question, together with certifications from Tenant's architect, certifying
that the work shown on the requisition has been performed in accordance with
applicable law and in accordance with Tenant's approved plans.

      (ii) Except with respect to work and/or materials previously paid for by
Tenant, as evidenced by paid invoices provided to Landlord, Landlord shall have
the right to have Landlord's Contribution paid to both Tenant and Tenant's
contractor(s) and vendor(s) jointly, or directly to Tenant's contractor if
Landlord has reason to believe there are or may be outstanding claims by such
contractor(s) or vendor(s).

      (iii) Notwithstanding clauses (i) and (ii) above, to the extent not
previously requisitioned by Tenant as aforesaid, Landlord's Contribution shall
be applied towards the Yearly Rent payable for and with respect to the months of
March, April, and May of 2005, until the Landlord's Contribution has been
exhausted.

      D. Except for Landlord's Contribution, Tenant shall bear all other costs
of Tenant's Work. Landlord shall have no liability or responsibility for any
claim, injury or damage alleged to have been caused by the particular materials,
whether building standard or non-building standard, selected by Tenant in
connection with Tenant's Work.

      5. TENANT'S OPTION TO EXTEND THE TERM OF THE LEASE

      Tenant shall continue to have one (1) five (5) year option to extend the
term of the Lease, pursuant to Paragraphs 1 and 4 of the Rider to Lease. To
reflect same, Paragraph 1.A of the Rider to Lease is deleted in its entirety and
the following is substituted in its place:

      "On the conditions, which conditions Landlord may waive, at its election,
by written notice to Tenant at any time, that Tenant is not in default after
notice thereof and the expiration of any applicable grace period(s) under
Article 21.7 without cure of its covenants and obligations under this Lease at
the time of option exercise (provided, however, that Tenant may cure any such
default at the time of option exercise), and that Forrester Research, Inc., an
Affiliate of Tenant and/or a Permitted Tenant Successor, as

                                      -6-
<PAGE>

such terms are defined in Article 16 of this Lease (such entities, collectively,
the "Original Tenant Entities"), collectively are occupying at least 84,505
square feet of Total Rentable Area of the Premises then demised to Tenant
("Occupancy Condition"), as of the commencement of the hereinafter described
additional term, Tenant shall have the option to extend the term of this Lease
for one (1) additional five (5) year term, such additional term commencing as of
the expiration of the initial term of this Lease. For the purposes of the
preceding sentence, the Original Tenant Entities shall be deemed to be
"occupying" space in the Premises if such space is subject to this Lease and has
not been sublet to any entity other than the Original Tenant Entities, provided
that the Original Tenant Entities actually occupy and conduct business in not
less than 62,379 square feet of Total Rentable Area of the Premises. Tenant may
exercise such option to extend by giving Landlord written notice on or before
the date twelve (12) months prior to the expiration date of the then current
term of this Lease. Upon the timely giving of such notice, the term of this
Lease shall be deemed extended upon all of the terms and conditions of this
Lease, except that Landlord shall have no obligation to construct or renovate
the Premises and that the Yearly Rent, Operating Costs in the Base Year, and Tax
Base during such additional term shall be as hereinafter set forth. If Tenant
fails to give timely notice, as aforesaid, Tenant shall have no further right to
extend the term of this Lease, time being of the essence of this Paragraph 1."

      The phrase "two (2) additional five (5) year terms" in Paragraph 1.D. of
the Rider to Lease is deleted and the phrase "one (1) additional five (5) year
term" is substituted in its place.

      6. TENANT'S RIGHT OF FIRST OFFER

      On the conditions (which conditions Landlord may waive, at its election,
by written notice to Tenant at any time) that Tenant is not in default after
notice thereof and expiration of any applicable grace period(s) under Article
21.7 without cure of its covenants and obligations under the Lease and that the
Original Tenant Entities are meeting the Occupancy Condition, as defined in
Paragraph 5 above, both at the time that Landlord is required to give Landlord's
Notice, as hereinafter defined, and as of the Term Commencement Date in respect
of the RFO Premises, Tenant shall have the following right to lease the RFO
Premises, as hereinafter defined, when the RFO Premises become available for
lease to Tenant, as hereinafter defined, all upon and subject to the terms and
provisions of this Paragraph 5.

      A. Definition of RFO Premises

      "RFO Premises" shall be defined as each area above the first (1st) floor
of the Building that is the subject of a lease and shall be deemed to be
"available for lease to Tenant" if, during the term of the Lease, the term of
the then current lease of such area (as such term may be extended or renewed
pursuant to any extension or renewal option contained in such lease) has expired
or been terminated. In no event shall Tenant have any rights under this
Paragraph 5 on or after the date twelve (12) months prior to the expiration of
the term of the Lease (i.e. Landlord shall have no obligation to give

                                      -7-
<PAGE>

Landlord's Notice, as hereinafter defined, to Tenant on or after the date twelve
(12) months prior to the expiration of the term of the Lease as the same may
have been extended). Notwithstanding anything to the contrary in this Paragraph
6, Floor 9 of the Building shall not be deemed to be "available for lease to
Tenant" if Landlord elects to extend or renew the term of the lease of
Frictionless Commerce Incorporated ("Frictionless"), any affiliate of
Frictionless, any successor by merger to Frictionless, or any entity that
acquires substantially all of the stock or assets of Frictionless, whether or
not such extension or renewal is made pursuant to any extension or renewal
option contained in the existing lease with Frictionless or if Landlord elects
to enter a new lease of such space with Frictionless or any of the foregoing
entities, and Landlord may enter into any such transaction without giving Tenant
Landlord's Notice, as hereinafter defined, and the subject premises shall not be
deemed "available for lease to Tenant" until any lease to Frictionless or any of
the foregoing entities expires or is terminated without extension or renewal or
aforesaid.

      B. Exercise of Right to Lease RFO Premises

            Landlord shall give Tenant written notice ("Landlord's Notice") not
sooner than twelve (12) months or, except in the event of an early termination
of the subject lease, later than three (3) months before an RFO Premises will
become available for lease to Tenant. Landlord's Notice shall set forth the
exact location of the RFO Premises and Landlord's designation of the Fair Market
Rental Value (as defined in Paragraph 4 of the Rider to Lease) applicable to the
RFO Premises. Tenant shall have the right, exercisable upon written notice
("Tenant's Exercise Notice") given to Landlord within fourteen (14) days (or, in
the event of an early termination of a lease of any RFO Premises, thirty (30)
days) after the receipt of Landlord's Notice, to lease the RFO Premises. If
Tenant fails timely to give Tenant's Exercise Notice, Tenant shall have no
further right to lease such RFO Premises pursuant to this Paragraph 5, provided
however, that (i) Landlord shall not lease such RFO Premises to any entity
(other than any of the Original Tenant Entities) at a net effective rent (i.e.,
taking into account rent, free rent, allowances and any other concessions or
material economic differences in the transactions) to Landlord that is less than
ninety percent (90%) of Landlord's designation of Fair Market Rental Value set
forth in Landlord's Notice (calculated on a net effective rent basis, as
aforesaid) without first giving Tenant another Landlord's Notice setting forth
such lower rent, (ii) Landlord shall not lease such RFO Premises to any entity
(other than any of the Original Tenant Entities) at any rent, which lease is
executed more than nine (9) months after the date of the most recently delivered
Landlord's Notice with respect to such RFO Premises without first giving Tenant
another Landlord's Notice for and with respect to such RFO Premises (but in the
event Landlord gives Tenant a second or subsequent Landlord's Notice with
respect to such RFO Premises, as required by this clause (ii) within four (4)
months after the expiration of such nine- month period, then, notwithstanding
the foregoing, Tenant shall only have five (5) business days after receipt of
such Landlord's Notice to give a Tenant's Exercise Notice with respect thereto),
and (iii) Tenant shall have the right from time to time thereafter throughout
the term of the Lease until Tenant's right to lease the RFO Premises has lapsed,
to receive a Landlord's Notice as to any RFO Premises that subsequently becomes
available for lease to Tenant upon the expiration of such nine-

                                      -8-
<PAGE>

month period or the expiration or termination of the lease entered into for
such space (as such term may be extended or renewed pursuant to any extension or
renewal option contained in such lease). Upon the timely giving of Tenant's
Exercise Notice, Landlord shall automatically be deemed to have leased and
demised to Tenant and Tenant shall automatically be deemed to have hired and
taken from Landlord, such RFO Premises, upon all of the same terms and
conditions of this Lease including, without limitation, the provisions regarding
Tenant's Extension Option, except as hereinafter set forth.

      C. Lease Provisions Applying to RFO Premises

            The leasing to Tenant of such RFO Premises shall be upon all of the
same terms and conditions of the Lease, except as follows:

            (1) Term Commencement Date

            The Term Commencement Date in respect of such RFO Premises shall be
the latest of: (x) the date the subject RFO Premises is to become available for
lease to Tenant as set forth in Landlord's Notice, or (y) the date that Landlord
delivers such RFO Premises to Tenant or (z) in the event of an early termination
of a lease of the subject RFO Premises, thirty (30) days after the date
Landlord's Notice is received by Tenant. Landlord agrees to use commercially
reasonable efforts to deliver such RFO Premises to Tenant promptly after the
term of the lease of the then current occupant of such area, as such term may be
extended or renewed as aforesaid, has expired or been terminated, which efforts
shall include, if necessary, the commencement and prosecution of a summary
process action to recover possession of such space from such occupant.

            (2) Yearly Rent

            The Yearly Rent rental rate in respect of such RFO Premises shall be
based upon the Fair Market Rental Value, as defined in Paragraph 4 of the Rider
to Lease, of such RFO Premises as of the Term Commencement Date in respect of
such RFO Premises.

            (3) Condition of RFO Premises

            Tenant shall take such RFO Premises "as-is" in its then (i.e. as of
the date of premises delivery) state of construction, finish, and decoration,
without any obligation on the part of Landlord to construct or prepare any RFO
Premises for Tenant's occupancy.

      D. Subordinate Rights

      Except as provided in Subparagraph F below, Tenant's rights under this
Paragraph 6 are subordinate to the existing rights of Novartis Institutes for
BioMedical Research, Inc. ("Novartis") or any entity claiming by, through, or
under Novartis under its existing

                                      -9-
<PAGE>

leases of space in the Complex. Such existing rights are summarized on Exhibit B
attached hereto.

      E. Execution of Lease Amendments

            Notwithstanding the fact that Tenant's exercise of the
above-described option to lease RFO Premises shall be self-executing, as
aforesaid, the parties hereby agree promptly to execute a lease amendment
reflecting the addition of an RFO Premises. At the time that such Yearly Rent,
Building Operating Cost Base, Complex Operating Cost Base and Tax Base are
determined, the parties shall execute a written agreement confirming the same.
The execution of such lease amendment shall be deemed to waive any of the
conditions to Tenant's exercise of the herein option to lease the RFO Premises,
unless otherwise specifically provided in such lease amendment. The failure of
the parties to execute such lease amendment shall not affect the validity of any
exercise of the above-described option to lease RFO Premises.

      F. Floor 8 Rights

            Notwithstanding the foregoing, Landlord agrees that (i) Tenant's
rights under this Paragraph 6 with respect to Floor 8 of the Building are not
and shall not be subordinate to the rights of Novartis or any other tenant or
subtenant of the Building, (ii) Landlord shall give Tenant a Landlord's Notice
with respect to said Floor 8 on or before August 1, 2008, but not sooner than
August 1, 2007, and (iii) Landlord shall cause said Floor 8 to be available for
lease to Tenant on or before October 1, 2008. Landlord shall satisfy its
obligation under clause (iii) of the preceding sentence if Landlord does not
grant any entity (other than Tenant or any of the Named Tenant Entities) the
right to use or occupy said Floor 8 from and after October 1, 2008, except to
the extent that such right is subject to Tenant's rights hereunder, and Landlord
uses commercially reasonable efforts to cause the then occupant(s) of said Floor
8 to vacate same on or before October 1, 2008.

      7. INAPPLICABLE AND DELETED LEASE PROVISIONS

      A. Article 4 of the Lease, Exhibits 4 and 4A to the Lease, Paragraph 2 of
the Second Amendment shall have no applicability during the Additional Term.

      B. The last sentence of Article 2.3(a) of the Lease and Paragraphs 2, 3, 6
and 8 of the Rider to Lease are hereby deleted and are of no further force or
effect.

      8. BROKER

      (a) Tenant represents and warrants that it has not directly or indirectly
dealt, with respect to the leasing of space in the Building with any broker or
had its attention called to the premises or other space to let in the Building,
etc. by anyone other than CBRE/Lynch Murphy Walsh Advisors and Richards Barry
Joyce & Partners, LLC (the "Brokers"). Tenant agrees to defend, exonerate and
save harmless and indemnify

                                      -10-
<PAGE>

Landlord and anyone claiming by, through or under Landlord against any claims
for a commission arising in breach of the representation and warranty set forth
in the immediately preceding sentence.

      (b) Landlord shall be solely responsible for the payment of brokerage
commissions to the Brokers. Landlord represents and warrants that, in connection
with the execution and delivery of this Fifth Amendment, it has not directly or
indirectly dealt with any broker other than the Brokers. Landlord agrees to
defend, exonerate, save harmless, and indemnify Tenant and anyone claiming by,
through, or under Tenant against any claims arising in breach of the
representation and warranty set forth in the immediately preceding sentence.

      9. SIGNAGE

      Tenant shall continue to have the signage rights pursuant to Exhibit 10 of
the Lease; provided, however, that at such time, if any, as Forrester Research,
Inc. (the "Named Tenant") shall occupy less than 84,505 square feet of space in
the Building (i.e., four (4) full floors), then notwithstanding the provisions
of Paragraph 4 of Exhibit 10, Tenant shall have the right to erect and maintain
only one (1) Exterior Sign. In the event the Named Tenant is occupying less than
62,379 square feet, Tenant shall no longer have the right to erect and maintain
any of the Exterior Signs, pursuant to said Exhibit 10 of the Lease.

      10. LANDLORD'S DEFAULT

      A. Landlord shall not be deemed to be in default of its obligations under
the Lease unless Tenant has given Landlord written notice of such default, and
Landlord has failed to cure said default within thirty (30) days after Landlord
receives such notice or, assuming the same is susceptible of cure within a
reasonable period of time, such longer period of time as Landlord may reasonably
require to cure such default.

      B. Except as otherwise expressly provided in the Lease, in no event shall
Tenant have the right to terminate the Lease nor, except as expressly otherwise
provided in the Lease, shall Tenant's obligation to pay Yearly Rent or other
charges under the Lease abate based upon any default by Landlord of its
obligations under the Lease.

      11. REVISED TOTAL RENTABLE AREA OF THE COMPLEX

      Pursuant to the definition of "Complex" in Exhibit 1 to the Lease, the
Total Rentable Area of the Complex may change from time to time. Therefore, the
Total Square Footage of each of the buildings located within the Complex is
revised and is as set forth on Exhibit A attached hereto.

      12. As hereby amended, the Lease is ratified, confirmed and approved in
all respects.

                                      -11-
<PAGE>

      EXECUTED UNDER SEAL as of the date first above written.

LANDLORD:                                                     TENANT:
TECHNOLOGY SQUARE FINANCE, LLC               FORRESTER RESEARCH, INC.
By: Massachusetts Institute of Technology,
its manager

By: /s/_____________________                 By: /s/___________________________
Name: ______________________                         (Name) (Title)
Title: _______________________                       Hereunto Duly Authorized

Date Signed: _________________               Date Signed: _____________________

                                      -12-
<PAGE>

                                    EXHIBIT A

                       TOTAL RENTABLE AREA OF THE COMPLEX

                               TECHNOLOGY SQUARE
                    BUILDING AND CAMPUS TOTAL RENTABLE SPACE
                                (December 2004)

<TABLE>
<CAPTION>
      BUILDING                 RENTABLE SQ. FT.
---------------------          ----------------
<S>                            <C>
TECHNOLOGY SQUARE 100              255,441
TECHNOLOGY SQUARE 200              155,090
TECHNOLOGY SQUARE 300              175,609
TECHNOLOGY SQUARE 400              194,776
TECHNOLOGY SQUARE 500              178,664
TECHNOLOGY SQUARE 600              128,224
TECHNOLOGY SQUARE 700               48,930
                                  ---------
Total Complex Rentable Sq. Ft     1,136,734
                                  =========
</TABLE>

                                      -13-
<PAGE>

                                    EXHIBIT B

                 SUMMARY OF NOVARTIS EXPANSION/EXTENSION RIGHTS

Novartis currently has a right of first offer to lease whole floors of the
Building (up to a maximum of 155,000 rentable square feet in the aggregate in
the Complex).

                                      -14-