Notwithstanding any other provisions of this chapter, a safety member who enters the system with credit for prior service and retires upon completion of 20 years of continuous service and a total of 25 years of service after attaining age 50 whose retirement allowance is less than one-half of his or her final compensation, his or her prior service pension shall be increased so as to cause his or her total retirement allowance to amount to one-half of that final compensation.