Looking further this can be solved for a string target in patch.dict which can be resolved again while calling the decorated function. There could be a case where the actual target is specified and in that case mock could only updates the reference and cannot track if the variable has been redefined to reference a different dict object. In the below case also it's resolved with {'a': 1} in the decorator and later redefining target to {'a': 2} whose reference is not updated. I can propose a PR for string target but I am not sure if this case can be solved or it's expected. This seems to be not a problem with patch.object where redefining a class later like dict seems to work correctly and maybe it's due to creating a new class itself that updates the local to reference new class? Any thoughts would be helpful. # script with dict target passed from unittest import mock target = dict(a=1) @mock.patch.dict(target, dict(b=2)) def test_with_decorator(): print(f"target inside decorator : {target}") def test_with_context_manager(): with mock.patch.dict(target, dict(b=2)): print(f"target inside context : {target}") target = dict(a=2) test_with_decorator() test_with_context_manager() $ ./python.exe test_foo.py target inside decorator : {'a': 2} target inside context : {'a': 2, 'b': 2}