40 ILCS 5/9-153

In any case in which an employee's credit for an annuity for himself or his widow is insufficient - at the time the annuity is fixed, - to provide an immediate life annuity of $150 a month for the employee or his widow, a term annuity of equal actuarial value of $150 a month shall be paid for such time as such payments can be made from such credits for the respective annuities.