How to extend the validity of a fixed-term employment contract for an indefinite period?

If the fixed-term contract has expired and the person continues to work, then such contract is considered extended for an indefinite period.

According to Art. 39-1 of the Labor Code, if after the expiration of the employment contract the employment relationship actually continues and none of the parties demands its termination, the validity of this contract is considered to be extended for an indefinite period.