Experience clearly suggests that most legal philosophers and ethicists are not surprised to be told that liberal states cannot permissibly prohibit same-sex marriage (henceforth: SSM). It is somewhat less clear just what the appropriate liberal strategy is and should be in defense of this thesis. Rather than try to defend SSM directly, I shall proceed indirectly by arguing that SSM prohibitions are indefensible on liberal grounds. Initially, I shall consider what I take to be the most powerful liberal argument against SSM prohibitions and account for my reservations about it. Then, I shall propose an alternative argument with roots in constitutional law that since SSM prohibitions do not survive liberal scrutiny, they must be rejected.