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                                                                    EXHIBIT 4.21

          AMENDMENT TO SERIES A CAPITAL SECURITIES GUARANTEE AGREEMENT

                  This Amendment to Series A Capital Securities Guarantee
Agreement (the "Amendment") is made as of December 17, 1999 by and between
Olympia Financial Corp., a Delaware corporation, and The Bank of New York, a New
York banking corporation.

                                   WITNESSETH

                  WHEREAS, Olympia Financial Corp., successor by merger to
ONBANCorp, Inc., (the "Guarantor"), and The Bank of New York, as trustee (in
such capacity, the "Capital Securities Guarantee Trustee") previously entered
into a Series A Capital Securities Guarantee Agreement dated as of February 4,
1997 (the "Guarantee Agreement") by which the Guarantor agreed to make certain
payments to the Holders of Series A Capital Securities issued pursuant to an
Amended and Restated Declaration of Trust dated as of February 4, 1997 by and
between Guarantor, in its capacity as Sponsor, The Bank of New York, as property
trustee, and The Bank of New York (Delaware), a Delaware banking corporation, as
Delaware trustee; and

                  WHEREAS, ONBANCorp, Inc. has been merged with and into Olympia
Financial Corp., a wholly owned subsidiary of M&T Bank Corporation, a New York
corporation; and

                  WHEREAS, the Administrative Trustees of the Trust have changed
the name of the Trust from "OnBank Capital Trust I" to "M&T Capital Trust III;"
and

                  WHEREAS, the Guarantor and the Guarantee Trustee desire to
amend the Guarantee Agreement to provide for the change of the Guarantor from
"ONBANCorp, Inc." to "Olympia Financial Corp.," and the name of the Trust from
"OnBank Capital Trust I" to "M&T Capital Trust III."

                  NOW THEREFORE, in consideration of the agreements and
obligations set forth herein and for other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, each party to this
Amendment, for the benefit of the other parties and for the benefit of the
Holders, hereby amends the Guarantee Agreement, and agrees, intending to be
legally bound, as follows:

SECTION 1.  DEFINITIONS.

                  1.1. For all purposes of this Amendment, except as otherwise
expressly provided, terms used but not defined in this Amendment shall have the
meanings assigned to them in the Guarantee Agreement.

                  1.2. The definition of "Guarantor" in the preamble of the
Guarantee Agreement is amended to mean Olympia Financial Corp., a Delaware
corporation.


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                  1.3. The definition of "Issuer" in the preamble of the
Guarantee Agreement is amended to read "M&T Capital Trust III."

SECTION 2.  MISCELLANEOUS.

                  2.1. CONTINUING AGREEMENT. The Guarantee Agreement shall not
be amended by this Amendment except as specifically provided in this Amendment
and, amended as so specifically provided, the Guarantee Agreement shall remain
in full force and effect. References in the Guarantee Agreement to "this
Guarantee Agreement" shall be deemed to be references to the Guarantee Agreement
as amended by this Amendment.

                  2.2. CONFLICTS. In the event of a conflict between the terms
and conditions of the Guarantee Agreement and the terms and conditions of this
Amendment, the terms and conditions of this Amendment shall prevail.

                  2.3. COUNTERPART ORIGINALS. The parties may sign any number of
copies of this Amendment. Each signed copy shall be an original, but all of them
together represent the same agreement.

                  2.4. HEADINGS, ETC. The headings of the sections of this
Amendment have been inserted for convenience of reference only, are not to be
considered a part hereof, and shall in no way modify or restrict any of the
terms or provisions hereof.

                  IN WITNESS WHEREOF the parties have caused this Amendment to
be executed as of the day and year first above written.

                                    OLYMPIA FINANCIAL CORP.
                                    as Guarantor


                                    By:  /s/ Michael P. Pinto
                                       -----------------------------------
                                       Michael P. Pinto
                                       Chairman of the Board and President

                                    THE BANK OF NEW YORK
                                    as Guarantee Trustee,
                                    and not in its individual capacity

                                    By:  /s/ Iliana A. Arciprete
                                       -----------------------------------
                                       Iliana A. Arciprete
                                       Assistant Treasurer

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