Composite fading wireless channels possess both fast and slow fading dynamics. In such channels, the average bit error probability varies slowly over time, hence, it is feasible to harness a power control mechanism to effectively avoid the bit error outage (BEO). In this letter, we focus on a new adaptive power allocation scheme for M-ary phase shift keying ( M-PSK) signals. The proposed power control technique is designed to track the moments of the composite fading envelope. Analytical expressions are derived which provide the optimal transmit power (under long-term power constraint) and the minimum transmit power to cope with the BEO. Numerical results indicate that the transmit power can be potentially decreased depending on the fading gain observed in the coherent and diffuse components of the received signal.