40 ILCS 5/9-174

Contributions by disabled employee whose ordinary disability benefit has expired.

In the case of any disabled employee whose credit for ordinary disability benefit purposes has expired and who continues to be disabled such employee shall have the right to contribute to the fund at the current contribution rate for a period not to exceed a total of 12 months during his entire period of service and to receive credit for all annuity purposes for any such periods paid for. Such payment shall not affect the employee's resignation date for purposes of annuity.