Thanks for the bisection. It's not surprising that that's the culprit, and in other situations that's the right thing to do. I'm not sure how to address this without breaking other stuff -- maybe leave the ForwardRef if evaluating it doesn't work? But that's likely to have other subtle side effects -- we still want simple typos (or other reasons why a reference is legitimately broken) to go unchecked. Maybe singledispatch can catch the error and fall back on looking at bare __annotations__?