In recent years, it has been widely held that a blameless belief that what one is doing is right is a full excuse for the action; that it makes the action blameless. There has been a lot of debate about how much difference this should make to our practices of blaming. But that's often been because there is large disagreement about when a false moral belief is blameless, not because there is disagreement about the principle. I want to push back against the principle. One part of my argument will involve raising doubts about the notion of a full excuse. But the main part will be an argument that once we carefully attend to Aristotle's distinction between acting in ignorance of the wrongness of one's actions, and acting from that ignorance, it is very hard to find a version of the principle that is not subject to clear counterexamples. I'll conclude by suggesting some particular kinds of moral ignorance that might be excusing (if not fully exculpatory), and suggesting that the circumstances in which they arise will be very rare.