This article outlines an argument against religious belief: the X-claim argument. The argument is novel at least in the sense that it has not yet been clearly articulated or addressed before in the philosophical literature. However, the argument is closely related to two more familiar varieties of argument currently receiving philosophical attention, namely: (i) arguments from religious diversity, and (ii) naturalistic debunking arguments (e.g. Freudian, Marxist, and evolutionary). I set out the X-claim argument, show that it has some prima facie plausibility, distinguish it from these other two arguments with which it might easily be confused, and, finally, explain why it has some significant advantages over these more familiar arguments against religious belief.