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It is unknown why females mate with multiple males when mating is frequently costly and a single copulation often provides enough sperm to fertilize all a female's eggs. One possibility is that remating increases the fitness of offspring, because fertilization success is biased toward the sperm of high-fitness males. We show that female Drosophila pseudoobscura evolved increased remating rates when exposed to the risk of mating with males carrying a deleterious sex ratio–distorting gene that also reduces sperm competitive ability. Because selfish genetic elements that reduce sperm competitive ability are generally associated with low genetic fitness, they may represent a common driver of the evolution of polyandry.