40 ILCS 5/5-150

Whenever the sum to a policeman's credit for annuity for him or his widow is insufficient, at the time the amount of such annuity is fixed, to provide a life annuity of $10 a month, a term annuity of $10 a month shall be payable for a period of years and months to be computed from his credits according to the actuarial tables in use by the fund.