Combining single-dispatch and protocols

Question

I'm having some issues combining single-dispatch overloads with a protocol for structural typing based on having a specific attribute. I have constructed the following snippet to give an idea of what I'm attempting.

from typing_extensions import Protocol
from functools import singledispatch


class HasFoo(Protocol):
    foo: str


class FooBar:
    def __init__(self):
        self.foo = 'bar'


@singledispatch
def f(_) -> None:
    raise NotImplementedError


@f.register
def _(item: HasFoo) -> None:
    print(item.foo)


x = FooBar()
f(x)

The above raises the NotImplementedError instead of the print statement as desired. I've tried various modifications to the above with no success. Any help would be very appreciated.