Mich. Comp. Laws § 38.34
A disability retirant who has been or shall be reinstated in active service, as provided in section 33, shall from the date of such reinstatement again become a member of the retirement system. Upon reinstatement of such disability retirant to active service, any balance he may have in the pension reserve fund at the time of such reinstatement to active service, shall be transferred from the pension reserve fund to the employees' savings fund and credited to his individual account in the employees' savings fund. Any service, on the basis of which his retirement allowance was computed at the time of his retirement, shall be restored to full force and effect, and, except in the case of retirement for non-duty disability as provided in section 24, he shall be given service credit for the period of time he was out of service due to such disability.
MCL 38.34