According to a thesis that is familiar from the Kantian tradition, moral obligations are a source of “authoritative reasons” – reasons it would be “irrational to ignore.” This thesis has been thought incompatible with moral naturalism and it has been a premise in arguments both for the moral error theory and for moral constructivism. I reject the thesis, however, and, in this paper, I contend that several arguments that have been advanced in support of it are unsuccessful. I also argue that the thesis is in fact compatible with both moral realism and moral naturalism. Moral naturalists have nothing to fear from it.