How to use typing.Protocol with modules?

I'd like to define a protocol which could be satisfied by an object, which might be a module:

from typing import Protocol

class MyType(Protocol):
    def foo(self) -> int:
        ...


class MyClass:
    def foo(self) -> int:
        return 1

# this is OK
a = MyClass()  # type: MyType

import mymodule
# mymodule.py just contains 
# def foo() -> int:
#     return 42

# but this is not.
b = mymodule  # type: MyType
# mypy complains saying
# Incompatible types in assignment (expression has type Module, variable has type "MyType")


import inspect
print(inspect.signature(a.foo))
print(inspect.signature(b.foo))
# both print: () -> int

gist here: https://gist.github.com/hjwp/e322c86d14ce0b11f08b27d7b17f7791