EXHIBIT 10.4.6
                                                                  --------------


                            SIXTH AMENDMENT TO LEASE


LESSOR:           Athenaeum Property LLC

LESSEE:           Bitstream Inc.

DATE OF LEASE:    March 17, 1992;
                  (First Amendment September 7, 1993,
                  Second Amendment July 14, 1994,
                  Third Amendment July 15, 1994,
                  Fourth Amendment March 3, 1997, and
                  Fifth Amendment April 15, 1997)

PREMISES:         Athenaeum House, 215 First Street,
                  Cambridge, Massachusetts (the "Building")

         FOR GOOD AND VALUABLE  CONSIDERATION,  the receipt and  sufficiency  of
which  are  hereby  acknowledged,  the lease  originally  entered  into  between
Athenaeum  Realty  Nominee Trust as Lessor and Bitstream  Inc., a  Massachusetts
corporation,  as Lessee  dated  March 17,  1992,  and  amended  as listed  above
(collectively,  the "Lease"), is hereby further amended as follows as of July 1,
1997 (the "Effective Date"):

         1.       PARTIES.  The  parties  acknowledge  and agree that  Athenaeum
                  Property  LLC has assumed all  obligations  as Lessor and that
                  Bitstream  Inc.,  a  Delaware  corporation,  has  assumed  all
                  obligations as Lessee Under the Lease.

         2.       "ADDITIONAL  LEASED PREMISES." As of the Effective Date, 5,624
                  rentable square feet ("RSF"),  more or less, shall be added to
                  the Leased  Premises  on the second  floor of the  Building as
                  shown on Exhibit A hereto ("Additional Leased Premises").

         3.       TERM. The initial term of the Lease shall be extended  through
                  October 1, 2003 with respect to the Additional Leased Premises
                  added hereby,  and also the Expanded  Leased Premises that the
                  parties added by the Fourth Amendment.  The initial Lease term
                  shall remain  unchanged  with respect to all other space under
                  the Lease,  and continue to extend through  October 1, 1998 in
                  accordance with the Second Amendment, ss.6.

         4.       INCREASED RENT. The Base Rent for the Leased Premises shall be
                  increased  as of the  Effective  Date by $18.00  per  rentable
                  square foot of the Additional Leased Premises, or $101,232 per
                  year through








Sixth Amendment to Lease dated March 17, 1992       Effective Date: July 1, 1997
Athenaeum Property LLC and Bitstream Inc.                                 Page 2

                  the end of the said term. All other rental amounts in the 
                  Lease shall remain unchanged.

         5.       INCREASED RENT ADJUSTMENT.  The Rent Adjustment percentage for
                  Real Estate Taxes and Common Area  Operating  expenses in ss.5
                  of the Lease shall be increased from 7.68% percent to 9.65% as
                  of the Effective Date.

         6.       UTILITIES.   All  Lessee's   utilities  will  continue  to  be
                  separately metered, or billed on a pro rata basis.

         7.       OPTIONS TO EXTEND.  The  parties  confirm and agree as follows
                  with  respect  to the  option to extend the term of the Leased
                  Premises in ss.23 of the original lease:

                  7.1.     Original Leased  Premises.  The option to extend with
                           respect  to  the  Leased   Premises  other  than  the
                           Expanded  Leased   Premises  and  Additional   Leased
                           Premises  (i.e.  17,174 RSF) shall  remain  unchanged
                           hereby,  and is hereby  confirmed  to consist of two,
                           consecutive  five (5) year  extensions,  the first to
                           begin  on  October  1,  1998 in  accordance  with the
                           Second Amendment,ss.6, and the second to begin on the
                           fifth anniversary  thereof,  or October 1,2003,  each
                           option to be exercised  within the  appropriate  time
                           period as provided in the  saidss.23  of the original
                           lease,  and the rent to be  determined  in accordance
                           with the formula stated in the saidss.23 on pp. 15-17
                           of the original lease.

                  7.2      Expanded and Additional Leased Premises.  There shall
                           be only one,  five year  option to extend the term of
                           the  "Expanded"  and  "Additional"   Leased  Premises
                           (4,700 RSF and 5,624 RSF, respectively), beginning on
                           October 1,2003, and upon written notice from LESEE to
                           LESSOR  at  least  six  (6)   months   prior  to  the
                           expiration of the initial lease term  (September  30,
                           2003).  The rental amount as of the  commencement  of
                           the  extended  term  shall  be fair  market  value as
                           determined in accordance with the procedure set forth
                           in the eighth full paragraph of ss.23 of the original
                           lease,  beginning  at the  bottom  of  page  15,  and
                           continuing through the top of page 17 thereof.

         8.       CONDITION OF ADDITIONAL  LEASED PREMISES.  Lessee agrees it is
                  leasing the  Additional  Leased  Premises "as is," except that
                  the Additional  Leased Premises shall be delivered  vacant and
                  free of rights of  possession or  occupancy,  vacuumed  clean,
                  free of debris and  personal  effects,  and all  systems to be
                  maintained  by  Landlord  under  the  Lease  shall  be in good
                  working order.

         9.       BROKER.  The Lessor and Lessee each  represent  and warrant to
                  the  other  hat each  has had no  dealings  with  any  Brokers
                  concerning  this lease other than  Robert A. Jones & Co.,  and
                  each party agrees








Sixth Amendment to Lease dated March 17, 1992       Effective Date: July 1, 1997
Athenaeum Property LLC and Bitstream Inc.                                 Page 3



                  to  indemnify  and hold the  other  harmless  for any  damages
                  occasioned  to  the  other  by  reason  of  a  breach  f  this
                  representation and warranty.

         10.      CONSTRUCTION;   INTERPRETATION.   To  the  extent   that  this
                  amendment  conflicts with the original  lease,  this amendment
                  shall control.  Both parties  acknowledge the lease remains in
                  full force and effect. Other than as stated in this amendment,
                  all other terms and conditions remain the same.




EXECUTED as a sealed instrument this 6th day of June 1997.

ATHENAEUM PROPERTY LLC



By:       /s/ Allan R. Jones                /s/ Geraldine McCarthy
    ---------------------------------       -------------------------
         Allan R. Jones, President          Witness
         Athenaeum F.A. Inc.
         Managing Member



BITSTREAM INC.



By:     /s/ James D. Hart                   /s/ John F. Dervishian
    ---------------------------------       -------------------------
         James D. Hart,                     Witness
         Vice President, Treasurer and
         Chief Financial Officer






                                    EXHIBIT A

                          "ADDITIONAL LEASED PREMESIS"


         A floor plan of consisting of 5,624 rentable  square feet on the second
floor of the property located at 215 First Street,  Cambridge,  Massachusetts is
set forth on this Exhibit.




THE ATHENAEUM HOUSE                                            Rev.
215 First Street, Cambridge         Second Floor               May 8, 1997