Exhibit 2.2

AGREEMENT TO VOTE SHARES

        This Agreement to Vote Shares relates to that certain Agreement and Plan of Merger dated as of May 11, 2005, among Firstbank Corporation, a Michigan corporation; Keystone Financial Corporation, a Michigan corporation; and Keystone Community Bank, a Michigan banking corporation (the “Agreement”). Capitalized terms used but not defined herein shall have the meanings assigned to them in the Agreement.

        The undersigned directors of Keystone hereby covenant and agree to vote the shares of Keystone Common Stock owned by them (including all shares of Keystone Common Stock over which such directors exercise direct or indirect voting control, including, but not limited to, a trust of which the shareholder is the grantor and trustee, a trust whose sole present beneficiaries are the shareholder’s family members or an individual retirement account (IRA) in the name of the shareholder), in favor of the Agreement at the Keystone Shareholders Meeting called to approve the Agreement.