--- a/requirements_dev.txt
+++ b/requirements_dev.txt
@@ -1,4 +1,3 @@
-mock==4.0.2
 flake8==3.8.3
 flake8-black==0.2.3
 pytest==6.2.5
--- a/tests/test_async.py
+++ b/tests/test_async.py
@@ -10,7 +10,7 @@ try:
 except ImportError:
     from concurrent.futures import TimeoutError  # type: ignore
 
-from mock import Mock
+from unittest.mock import Mock
 from twisted.internet.defer import succeed
 
 from pyee import AsyncIOEventEmitter, TwistedEventEmitter
--- a/tests/test_cls.py
+++ b/tests/test_cls.py
@@ -1,5 +1,5 @@
 # -*- coding: utf-8 -*-
-from mock import Mock
+from unittest.mock import Mock
 import pytest
 
 from pyee import EventEmitter
--- a/tests/test_executor.py
+++ b/tests/test_executor.py
@@ -2,7 +2,7 @@
 
 from time import sleep
 
-from mock import Mock
+from unittest.mock import Mock
 
 from pyee import ExecutorEventEmitter
 
--- a/tests/test_sync.py
+++ b/tests/test_sync.py
@@ -1,7 +1,7 @@
 # -*- coding: utf-8 -*-
 from collections import OrderedDict
 
-from mock import Mock
+from unittest.mock import Mock
 from pytest import raises
 
 from pyee import EventEmitter
--- a/tests/test_twisted.py
+++ b/tests/test_twisted.py
@@ -1,6 +1,6 @@
 # -*- coding: utf-8 -*-
 
-from mock import Mock
+from unittest.mock import Mock
 from twisted.internet.defer import inlineCallbacks
 from twisted.python.failure import Failure
 
--- a/tests/test_uplift.py
+++ b/tests/test_uplift.py
@@ -1,6 +1,6 @@
 # -*- coding: utf-8 -*-
 
-from mock import call, Mock
+from unittest.mock import call, Mock
 import pytest
 
 from pyee import EventEmitter