TypeError: unbound method when trying to mock a classmethod

This scripts fails:

import mock

class MyClass(object):

    @classmethod
    def my_method(cls):
        print('my_method')

def mocked_method(cls):
    print('I want this method to get called')

with mock.patch.object(MyClass, 'my_method', mocked_method):
    MyClass.my_method()

Exception:

Traceback (most recent call last):
  File "/home/foo/tmp/test_mocking_classmethod.py", line 14, in <module>
    MyClass.my_method()
TypeError: unbound method mocked_method() must be called with MyClass instance as first argument (got nothing instead)