In diversity combining automatic repeat request (ARQ), erroneous packets are combined together forming a single, more reliable, packet. In this paper, we give a diversity combining scheme for the m-ary unidirectional channel. A system using the given scheme with a t-unidirectional error detecting code is able to correct up to Emax = [t/2] unidirectional errors. Simulation results show that the underlined diversity combining protocol significantly increases the channel throughput over plain ARQ. To use the given scheme, the decoder should be able to decide the error type (increasing or decreasing). Hence, we give simple techniques to make this decision for various unidirectional error detecting codes.