Using a pipe symbol in typing.Literal string

I have a function that accepts certain literals for a specific argument:

from typing import Literal

def fn(x: Literal["foo", "bar", "foo|bar"]) -> None:
    reveal_type(x)

The third contains a pipe symbol (|), "foo|bar". This is interpreted by mypy as an error, as the name foo is not defined.

I guess this happens due to how forward references are evaluated? I use Python 3.8 with:

from __future__ import annotations

Is there a way to make this work? I can not change the string due to breaking backward compatibility, but currently, the whole annotation is revealed as Any, i.e. it holds no value.