This paper presents a simple DPSK receiver for the frequency-selective fading channel. The channel is modelled as an f-power series truncated to the first two terms [1,2]. Two time invariant receiver filters are used to remove the channel induced ISI and to separate the two implicit diversity branches. The received samples from each branch are then differentially decoded and combined. Analytical and simulation results for binary DPSK show that this receiver outperforms the conventional receiver using matched filtering and a product demodulator.