https://github.com/python/mypy/labels/topic-typeguard https://github.com/python/mypy/labels/topic-type-variables ```py from typing import TypeGuard, TypeVar, Callable T = TypeVar("T") def guard(x: object) -> TypeGuard[str]: return True def f(fn: Callable[[object], T]) -> T: return fn(1) reveal_type(f(guard)) # Any ``` This should be `bool`, not `Any` - Follow on from #17114