<PAGE>

                     ACKNOWLEDGEMENT OF ASSUMPTION OF LEASE

      ACKNOWLEDGEMENT OF ASSUMPTION OF LEASE dated as of this 28 day of June,
1999, by and among BOSTON PROPERTIES LIMITED PARTNERSHIP (as
successor-in-interest to the Trustees of 91 Hartwell Avenue Trust, "Landlord"),
MOLDFLOW PTY. LTD, an Australian corporation registered to do business in
Connecticut ("Assignor") and MOLDFLOW CORPORATION, a Delaware corporation
("Assignee").

                                 R E C I T A L S

      By Lease dated October 15, 1996 (the "Lease"), Landlord did lease to
Assignor and Assignor did lease from Landlord certain premises in the building
known as and numbered 91 Hartwell Avenue, Lexington, Massachusetts, all as more
specifically described in the Lease (hereinafter referred to as the "Premises").

      Effective as of July 1, 1999, Assignor will assign and Assignee will
assume all of Assignor's liabilities, rights and obligations under the Lease
(such assumption by Assignee being hereinafter referred to as the "Assumption").

      Landlord desires to acknowledge Assignee's assumption of Assignor's
obligations under the Lease upon the terms and conditions contained in this
Acknowledgement of Assumption of Lease (the "Acknowledgment").

      NOW, THEREFORE, in consideration of One Dollar ($1.00) and other good and
valuable consideration, paid by each of the parties hereto to the other, the
receipt and sufficiency of which are hereby acknowledged, and in further
consideration of the provisions herein, Landlord, Assignor and Assignee hereby
agree as follows:

1.    Landlord, Assignor and Assignee hereby acknowledge and agree that the
      Assumption constitutes an assignment by Assignor and an assumption by
      Assignee of Assignor's rights and obligations under Section 5.6.1 of the
      Lease.

2.    Assignee shall be directly bound and fully liable to Landlord for all of
      the obligations of Assignor under the Lease, both prior to and subsequent
      to the Assumption, including, without limitation, the obligation to pay
      rent, additional rent and all other charges in the full amount, in the
      manner and at the times provided for under the Lease.


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3.    Notwithstanding the provisions of Section 5.6.6 of the Lease regarding the
      joint and several liability of Assignor and Assignee (which such
      provisions are expressly waived by Landlord in connection with this
      Assumption), Landlord hereby releases and discharges Assignor from any
      obligations and responsibilities under the Lease effective as of July 1,
      1999.

4.    Landlord's execution of this Acknowledgement shall not constitute a
      consent or acknowledgement to any future assignment of the Lease or
      subletting of the Premises which shall be subject to the terms of Sections
      5.6 through 5.6.6.

5.    All capitalized terms and words used in this instrument shall have the
      same meaning as set forth in the Lease unless a contrary meaning is
      expressly set forth herein.

6.    Except as expressly provided herein, the Lease and the terms and
      provisions thereof, shall remain unchanged and in full force and effect.

7.    This Acknowledgment may be executed in several counterparts, each of which
      shall be deemed to be an original but all of which shall constitute one
      and the same agreement.


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      EXECUTED under seal as of the date and year first above written.


                                              LANDLORD

                                              BOSTON PROPERTIES LIMITED
                                              PARTNERSHIP

                                              By: Boston Properties, Inc., its
                                                  general partner


                                                  By: /s/ Stacey A. Baker
                                                      --------------------------
                                                  Name: Stacey A. Baker
                                                        ------------------------
                                                  Title: Vice President
                                                         -----------------------

                                              ASSIGNOR

                                              MOLDFLOW PTY. LTD


                                              By: /s/ Marc Dulude
                                                  ------------------------
                                              Name: Marc Dulude
                                                    ----------------------
                                              Title: Director
                                                     ---------------------

                                              ASSIGNEE:

                                              MOLDFLOW CORPORATION


                                              By: /s/ Suzanne E. Rogers
                                                  ------------------------
                                              Name: Suzanne E. Rogers
                                                    ----------------------
                                              Title: Vice President
                                                     ---------------------


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