Mock python decorator in unit tests

I am trying to test a function that is decorated. Is there a way to mock a decorator and test function in isolation, when decorator is already applied?

import mock


def decorator(func):
    def wrapper(*args, **kwargs):
        return 1
    return wrapper


def mocked(func):
    def wrapper(*args, **kwargs):
        return 2
    return wrapper


@decorator
def f():
    return 0


with mock.patch('test.decorator') as d:
    d.side_effect = mocked
    assert f() == 2  # error