Moore's Open Question Argument has been heavily debated ever since it was presented over 100 years ago. In the current paper, it is argued that for the realist, and contrary to the received view by many theorists in the debate, the argument in fact lends strong support for non-naturalism. In particular, David Brink's naturalist defense utilizing direct reference theory is scrutinized. It is argued that an application of direct reference to moral kinds, rather than defusing the Open Question Argument, actually (...) underscores the non-naturalist conclusion. The naturalist argument depends heavily on the analogue between natural kinds and moral kinds. It is argued that the Open Question Argument provides prima facie evidence against the idea that moral kinds are natural kinds, and that the naturalist arguments do not overturn this evidence. Moreover, it is argued that similar reasons to those which render direct reference unviable for moral terms also meet two further potential objections against the Open Question Argument, and it is concluded that the argument carries considerable force against the moral naturalist. (shrink)