diff --git a/CHANGES b/CHANGES
index f6e834b3a..f09d178ef 100644
--- a/CHANGES
+++ b/CHANGES
@@ -44,6 +44,11 @@ Bugs fixed
 * #3038: ``sphinx.ext.math*`` raises TypeError if labels are duplicated
 * #3031: incompatibility with LaTeX package ``tocloft``
 
+Testing
+--------
+
+* To simplify, sphinx uses external mock package even if unittest.mock exists.
+
 Documentation
 -------------
 
diff --git a/tests/test_build.py b/tests/test_build.py
index 27a99461b..cc34de2c1 100644
--- a/tests/test_build.py
+++ b/tests/test_build.py
@@ -13,11 +13,12 @@ from six import BytesIO
 
 import pickle
 from docutils import nodes
+import mock
 from textwrap import dedent
 from sphinx.errors import SphinxError
 import sphinx.builders.linkcheck
 
-from util import mock, with_app, with_tempdir, rootdir, tempdir, SkipTest, TestApp
+from util import with_app, with_tempdir, rootdir, tempdir, SkipTest, TestApp
 
 try:
     from docutils.writers.manpage import Writer as ManWriter
diff --git a/tests/test_config.py b/tests/test_config.py
index b10711732..1b3c94957 100644
--- a/tests/test_config.py
+++ b/tests/test_config.py
@@ -10,7 +10,7 @@
     :license: BSD, see LICENSE for details.
 """
 from six import PY3, iteritems
-from util import mock
+import mock
 
 from util import TestApp, with_app, gen_with_app, with_tempdir, \
     raises, raises_msg, assert_in, assert_not_in
diff --git a/tests/test_domain_std.py b/tests/test_domain_std.py
index 5bd9f805b..4f892cb01 100644
--- a/tests/test_domain_std.py
+++ b/tests/test_domain_std.py
@@ -10,9 +10,9 @@
 """
 
 from docutils import nodes
+import mock
 
 from sphinx.domains.std import StandardDomain
-from util import mock
 
 
 def test_process_doc_handle_figure_caption():
diff --git a/tests/test_environment_indexentries.py b/tests/test_environment_indexentries.py
index 869239487..57a3cf52f 100644
--- a/tests/test_environment_indexentries.py
+++ b/tests/test_environment_indexentries.py
@@ -13,7 +13,7 @@ from collections import namedtuple
 from sphinx import locale
 from sphinx.environment.managers.indexentries import IndexEntries
 
-from util import mock
+import mock
 
 Environment = namedtuple('Environment', 'indexentries')
 
diff --git a/tests/test_ext_intersphinx.py b/tests/test_ext_intersphinx.py
index 2b67dd329..e1995e3d3 100644
--- a/tests/test_ext_intersphinx.py
+++ b/tests/test_ext_intersphinx.py
@@ -15,6 +15,7 @@ import zlib
 
 from six import BytesIO
 from docutils import nodes
+import mock
 
 from sphinx import addnodes
 from sphinx.ext.intersphinx import setup as intersphinx_setup
@@ -22,7 +23,7 @@ from sphinx.ext.intersphinx import read_inventory, \
     load_mappings, missing_reference, _strip_basic_auth, _read_from_url, \
     _get_safe_url, fetch_inventory, INVENTORY_FILENAME
 
-from util import with_app, with_tempdir, mock
+from util import with_app, with_tempdir
 
 
 inventory_v1 = '''\
diff --git a/tests/test_ext_napoleon.py b/tests/test_ext_napoleon.py
index d4ce96001..7ecd08292 100644
--- a/tests/test_ext_napoleon.py
+++ b/tests/test_ext_napoleon.py
@@ -16,7 +16,7 @@ from unittest import TestCase
 from sphinx.application import Sphinx
 from sphinx.ext.napoleon import (_process_docstring, _skip_member, Config,
                                  setup)
-from util import mock
+import mock
 
 
 def _private_doc():
diff --git a/tests/test_ext_napoleon_docstring.py b/tests/test_ext_napoleon_docstring.py
index c320a7fec..37dcca90c 100644
--- a/tests/test_ext_napoleon_docstring.py
+++ b/tests/test_ext_napoleon_docstring.py
@@ -19,7 +19,7 @@ from unittest import TestCase
 
 from sphinx.ext.napoleon import Config
 from sphinx.ext.napoleon.docstring import GoogleDocstring, NumpyDocstring
-from util import mock
+import mock
 
 
 class NamedtupleSubclass(namedtuple('NamedtupleSubclass', ('attr1', 'attr2'))):
diff --git a/tests/test_theming.py b/tests/test_theming.py
index d4c104c8c..b62cbcd72 100644
--- a/tests/test_theming.py
+++ b/tests/test_theming.py
@@ -12,9 +12,11 @@
 import os
 import zipfile
 
+import mock
+
 from sphinx.theming import Theme, ThemeError
 
-from util import with_app, raises, mock, path
+from util import with_app, raises, path
 
 
 @with_app(confoverrides={'html_theme': 'ziptheme',
diff --git a/tests/test_util_fileutil.py b/tests/test_util_fileutil.py
index a56543614..5810dd2a8 100644
--- a/tests/test_util_fileutil.py
+++ b/tests/test_util_fileutil.py
@@ -11,14 +11,14 @@
 from sphinx.util.fileutil import copy_asset, copy_asset_file
 from sphinx.jinja2glue import BuiltinTemplateLoader
 
-from mock import Mock
+import mock
 from util import with_tempdir
 
 
 class DummyTemplateLoader(BuiltinTemplateLoader):
     def __init__(self):
         BuiltinTemplateLoader.__init__(self)
-        builder = Mock()
+        builder = mock.Mock()
         builder.config.templates_path = []
         builder.app.translater = None
         self.init(builder)
diff --git a/tests/util.py b/tests/util.py
index a14bee838..120492d47 100644
--- a/tests/util.py
+++ b/tests/util.py
@@ -28,12 +28,6 @@ from sphinx.pycode import ModuleAnalyzer
 
 from path import path, repr_as  # NOQA
 
-try:
-    # Python >=3.3
-    from unittest import mock
-except ImportError:
-    import mock
-
 
 __all__ = [
     'rootdir', 'tempdir', 'raises', 'raises_msg',
@@ -41,7 +35,6 @@ __all__ = [
     'ListOutput', 'TestApp', 'with_app', 'gen_with_app',
     'path', 'with_tempdir',
     'sprint', 'remove_unicode_literals',
-    'mock',
 ]
 
 
diff --git a/tox.ini b/tox.ini
index 5c5989250..44ae8a7a6 100644
--- a/tox.ini
+++ b/tox.ini
@@ -9,38 +9,30 @@ deps=
     sqlalchemy
     whoosh
     html5lib
+    mock
 setenv =
     SPHINX_TEST_TEMPDIR = {envdir}/testbuild
 commands=
     {envpython} tests/run.py -I py35 -m '^[tT]est' {posargs}
     sphinx-build -q -W -b html -d {envtmpdir}/doctrees doc {envtmpdir}/html
 
-[testenv:py27]
-deps=
-    mock
-    {[testenv]deps}
-
 [testenv:pypy]
 deps=
-    mock
     simplejson
     {[testenv]deps}
 
 [testenv:du10]
 deps=
-    mock
     docutils==0.10
     {[testenv]deps}
 
 [testenv:du11]
 deps=
-    mock
     docutils==0.11
     {[testenv]deps}
 
 [testenv:du12]
 deps=
-    mock
     docutils==0.12
     {[testenv]deps}