diff --git a/.circleci/config.yml b/.circleci/config.yml
index 6ae73bb..a5b583a 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -25,7 +25,7 @@ jobs:
                 virtualenv -p "$(which python || which pypy)" ./venv
             )
             . venv/bin/activate
-            pip install pytest mock
+            pip install pytest
       - run:
           name: Install project
           command: |
diff --git a/setup.py b/setup.py
index 8940285..ea154e1 100644
--- a/setup.py
+++ b/setup.py
@@ -11,7 +11,7 @@ setup(
     long_description_content_type='text/markdown',
     packages=find_packages(),
     install_requires=['six'],
-    tests_require=['pytest', 'mock', 'tox'],
+    tests_require=['pytest', 'tox'],
     zip_safe=True,
     classifiers=[
         'Development Status :: 5 - Production/Stable',
diff --git a/tests/test_gsm.py b/tests/test_gsm.py
index b6641fd..7760dc4 100644
--- a/tests/test_gsm.py
+++ b/tests/test_gsm.py
@@ -1,6 +1,6 @@
 # -*- coding: utf8 -*-
 
-import mock
+from unittest.mock import patch
 from pytest import mark, raises
 
 from smpplib import consts
@@ -39,7 +39,7 @@ def test_make_parts_single(plaintext, encoding, expected_parts, expected_encodin
     ]),
 ])
 def test_make_parts_multiple(plaintext, expected):
-    with mock.patch('random.randint') as randint:
+    with patch('random.randint') as randint:
         randint.return_value = 0x42
         assert make_parts(plaintext) == (expected, consts.SMPP_ENCODING_DEFAULT, consts.SMPP_GSMFEAT_UDHI)
 
@@ -49,7 +49,7 @@ def test_make_parts_multiple(plaintext, expected):
     (b'12345', 2, [b'\x05\x00\x03\x42\x03\x0112', b'\x05\x00\x03\x42\x03\x0234', b'\x05\x00\x03\x42\x03\x035']),
 ])
 def test_make_parts_encoded(encoded_text, part_size, expected):
-    with mock.patch('random.randint') as randint:
+    with patch('random.randint') as randint:
         randint.return_value = 0x42
         assert make_parts_encoded(encoded_text, part_size) == expected