Several recent studies have suggested that F(1) hybrid male lethality in crosses between Drosophila melanogaster and D. simulans is due to a failure in dosage compensation, caused by incompatibilities between D. simulans dosage compensation proteins and the D. melanogaster X chromosome. Contrary to the predictions of this hypothesis, mutations in four essential D. melanogaster dosage compensation genes are shown here to moderately increase rather than decrease hybrid male viability.