diff --git a/.gitignore b/.gitignore
index fe89362..c9310dc 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,5 @@
 *.pyc
+.python-version
 .tox
 .eggs
 *.egg
diff --git a/setup.py b/setup.py
index 3e71c30..f968fc9 100644
--- a/setup.py
+++ b/setup.py
@@ -12,7 +12,7 @@ sys.path.insert(0, os.path.join(os.path.dirname(__file__), 'src'))  # noqa
 import flake8
 
 
-tests_require = ['mock >= 2.0.0', 'pytest']
+tests_require = ['pytest']
 
 requires = [
     "pyflakes >= 0.8.1, != 1.2.0, != 1.2.1, != 1.2.2, < 1.4.0",
@@ -20,6 +20,9 @@ requires = [
     "mccabe >= 0.5.0, < 0.6.0",
 ]
 
+if sys.version_info < (3, 5):
+    tests_require.append('mock >= 2.0.0')
+
 if sys.version_info < (3, 4):
     requires.append("enum34")
 
diff --git a/tests/integration/test_checker.py b/tests/integration/test_checker.py
index 1b8a3c5..73286a8 100644
--- a/tests/integration/test_checker.py
+++ b/tests/integration/test_checker.py
@@ -1,5 +1,8 @@
 """Integration tests for the checker submodule."""
-import mock
+try:
+    import mock
+except ImportError:
+    from unittest import mock
 import pytest
 
 from flake8 import checker
diff --git a/tests/unit/test_application.py b/tests/unit/test_application.py
index 6a3ef91..131592c 100644
--- a/tests/unit/test_application.py
+++ b/tests/unit/test_application.py
@@ -1,7 +1,10 @@
 """Tests for the Application class."""
 import optparse
 
-import mock
+try:
+    import mock
+except ImportError:
+    from unittest import mock
 import pytest
 
 from flake8.main import application as app
diff --git a/tests/unit/test_base_formatter.py b/tests/unit/test_base_formatter.py
index bb54358..0ae23f7 100644
--- a/tests/unit/test_base_formatter.py
+++ b/tests/unit/test_base_formatter.py
@@ -1,7 +1,10 @@
 """Tests for the BaseFormatter object."""
 import optparse
 
-import mock
+try:
+    import mock
+except ImportError:
+    from unittest import mock
 import pytest
 
 from flake8 import style_guide
diff --git a/tests/unit/test_checker_manager.py b/tests/unit/test_checker_manager.py
index e5562ef..0456c0e 100644
--- a/tests/unit/test_checker_manager.py
+++ b/tests/unit/test_checker_manager.py
@@ -1,7 +1,10 @@
 """Tests for the Manager object for FileCheckers."""
 import errno
 
-import mock
+try:
+    import mock
+except ImportError:
+    from unittest import mock
 import pytest
 
 from flake8 import checker
diff --git a/tests/unit/test_config_file_finder.py b/tests/unit/test_config_file_finder.py
index 3f321da..82c1fb9 100644
--- a/tests/unit/test_config_file_finder.py
+++ b/tests/unit/test_config_file_finder.py
@@ -3,7 +3,10 @@ import configparser
 import os
 import sys
 
-import mock
+try:
+    import mock
+except ImportError:
+    from unittest import mock
 import pytest
 
 from flake8.options import config
diff --git a/tests/unit/test_debug.py b/tests/unit/test_debug.py
index dbafe2e..9284ffe 100644
--- a/tests/unit/test_debug.py
+++ b/tests/unit/test_debug.py
@@ -1,5 +1,8 @@
 """Tests for our debugging module."""
-import mock
+try:
+    import mock
+except ImportError:
+    from unittest import mock
 import pytest
 import setuptools
 
diff --git a/tests/unit/test_file_checker.py b/tests/unit/test_file_checker.py
index a2d33fc..5208136 100644
--- a/tests/unit/test_file_checker.py
+++ b/tests/unit/test_file_checker.py
@@ -1,5 +1,8 @@
 """Unit tests for the FileChecker class."""
-import mock
+try:
+    import mock
+except ImportError:
+    from unittest import mock
 
 from flake8 import checker
 
diff --git a/tests/unit/test_file_processor.py b/tests/unit/test_file_processor.py
index c534003..4e875c6 100644
--- a/tests/unit/test_file_processor.py
+++ b/tests/unit/test_file_processor.py
@@ -5,7 +5,10 @@ import tokenize
 
 from flake8 import processor
 
-import mock
+try:
+    import mock
+except ImportError:
+    from unittest import mock
 import pytest
 
 
diff --git a/tests/unit/test_git.py b/tests/unit/test_git.py
index 24d4b5b..6a29fbc 100644
--- a/tests/unit/test_git.py
+++ b/tests/unit/test_git.py
@@ -1,5 +1,8 @@
 """Tests around functionality in the git integration."""
-import mock
+try:
+    import mock
+except ImportError:
+    from unittest import mock
 import pytest
 
 from flake8.main import git
diff --git a/tests/unit/test_legacy_api.py b/tests/unit/test_legacy_api.py
index 0f1d1f3..5929211 100644
--- a/tests/unit/test_legacy_api.py
+++ b/tests/unit/test_legacy_api.py
@@ -1,5 +1,8 @@
 """Tests for Flake8's legacy API."""
-import mock
+try:
+    import mock
+except ImportError:
+    from unittest import mock
 import pytest
 
 from flake8.api import legacy as api
diff --git a/tests/unit/test_merged_config_parser.py b/tests/unit/test_merged_config_parser.py
index 1541df4..7fe3084 100644
--- a/tests/unit/test_merged_config_parser.py
+++ b/tests/unit/test_merged_config_parser.py
@@ -1,7 +1,10 @@
 """Unit tests for flake8.options.config.MergedConfigParser."""
 import os
 
-import mock
+try:
+    import mock
+except ImportError:
+    from unittest import mock
 import pytest
 
 from flake8.options import config
diff --git a/tests/unit/test_option.py b/tests/unit/test_option.py
index 67e2255..843dea0 100644
--- a/tests/unit/test_option.py
+++ b/tests/unit/test_option.py
@@ -1,5 +1,8 @@
 """Unit tests for flake8.options.manager.Option."""
-import mock
+try:
+    import mock
+except ImportError:
+    from unittest import mock
 import pytest
 
 from flake8.options import manager
diff --git a/tests/unit/test_option_manager.py b/tests/unit/test_option_manager.py
index 661b445..483c3f0 100644
--- a/tests/unit/test_option_manager.py
+++ b/tests/unit/test_option_manager.py
@@ -2,7 +2,10 @@
 import optparse
 import os
 
-import mock
+try:
+    import mock
+except ImportError:
+    from unittest import mock
 import pytest
 
 from flake8 import utils
diff --git a/tests/unit/test_plugin.py b/tests/unit/test_plugin.py
index 84f676a..865af7e 100644
--- a/tests/unit/test_plugin.py
+++ b/tests/unit/test_plugin.py
@@ -1,7 +1,10 @@
 """Tests for flake8.plugins.manager.Plugin."""
 import optparse
 
-import mock
+try:
+    import mock
+except ImportError:
+    from unittest import mock
 import pytest
 
 from flake8 import exceptions
diff --git a/tests/unit/test_plugin_manager.py b/tests/unit/test_plugin_manager.py
index 8991b96..18bdced 100644
--- a/tests/unit/test_plugin_manager.py
+++ b/tests/unit/test_plugin_manager.py
@@ -1,5 +1,8 @@
 """Tests for flake8.plugins.manager.PluginManager."""
-import mock
+try:
+    import mock
+except ImportError:
+    from unittest import mock
 
 from flake8.plugins import manager
 
diff --git a/tests/unit/test_plugin_type_manager.py b/tests/unit/test_plugin_type_manager.py
index 186c2e3..6aef045 100644
--- a/tests/unit/test_plugin_type_manager.py
+++ b/tests/unit/test_plugin_type_manager.py
@@ -1,7 +1,10 @@
 """Tests for flake8.plugins.manager.PluginTypeManager."""
 import collections
 
-import mock
+try:
+    import mock
+except ImportError:
+    from unittest import mock
 import pytest
 
 from flake8 import exceptions
diff --git a/tests/unit/test_style_guide.py b/tests/unit/test_style_guide.py
index 7357b25..6b0f2aa 100644
--- a/tests/unit/test_style_guide.py
+++ b/tests/unit/test_style_guide.py
@@ -1,7 +1,10 @@
 """Tests for the flake8.style_guide.StyleGuide class."""
 import optparse
 
-import mock
+try:
+    import mock
+except ImportError:
+    from unittest import mock
 import pytest
 
 from flake8 import defaults
diff --git a/tests/unit/test_utils.py b/tests/unit/test_utils.py
index d1816bc..ded55cb 100644
--- a/tests/unit/test_utils.py
+++ b/tests/unit/test_utils.py
@@ -1,7 +1,10 @@
 """Tests for flake8's utils module."""
 import os
 
-import mock
+try:
+    import mock
+except ImportError:
+    from unittest import mock
 import pytest
 
 from flake8 import utils
diff --git a/tox.ini b/tox.ini
index b72f3ad..cc0fb34 100644
--- a/tox.ini
+++ b/tox.ini
@@ -4,14 +4,20 @@ envlist = py27,py33,py34,py35,flake8,linters,docs
 
 [testenv]
 deps =
-    mock>=2.0.0
     pytest
     coverage
+    mock>=2.0.0
 commands =
     coverage run --parallel-mode -m pytest {posargs}
     coverage combine
     coverage report -m
 
+[testenv:py35]
+# No mock needed on 3.5+
+deps =
+    pytest
+    coverage
+
 [testenv:venv]
 deps =
     .
@@ -31,7 +37,7 @@ commands =
 
 # Linters
 [testenv:flake8]
-basepython = python3
+basepython = python3.5
 skip_install = true
 deps =
     flake8
@@ -41,7 +47,7 @@ commands =
     flake8 src/flake8/ tests/ setup.py
 
 [testenv:pylint]
-basepython = python3
+basepython = python3.5
 skip_install = true
 deps =
     pyflakes
@@ -50,7 +56,7 @@ commands =
     pylint src/flake8
 
 [testenv:doc8]
-basepython = python3
+basepython = python3.5
 skip_install = true
 deps =
     sphinx
@@ -59,7 +65,7 @@ commands =
     doc8 docs/source/
 
 [testenv:mypy]
-basepython = python3
+basepython = python3.5
 skip_install = true
 deps =
     mypy-lang
@@ -67,7 +73,7 @@ commands =
     mypy flake8
 
 [testenv:bandit]
-basepython = python3
+basepython = python3.5
 skip_install = true
 deps =
     bandit
@@ -75,7 +81,7 @@ commands =
     bandit -r src/flake8/ -c .bandit.yml
 
 [testenv:linters]
-basepython = python3
+basepython = python3.5
 skip_install = true
 deps =
     {[testenv:flake8]deps}
@@ -92,7 +98,7 @@ commands =
 
 # Documentation
 [testenv:docs]
-basepython = python3
+basepython = python3.5
 deps =
     -rdocs/source/requirements.txt
 commands =
@@ -100,7 +106,7 @@ commands =
     sphinx-build -E -W -c docs/source/ -b man docs/source/ docs/build/man
 
 [testenv:serve-docs]
-basepython = python3
+basepython = python3.5
 skip_install = true
 changedir = docs/build/html
 deps =
@@ -108,7 +114,7 @@ commands =
     python -m http.server {posargs}
 
 [testenv:readme]
-basepython = python3
+basepython = python3.5
 deps =
     readme_renderer
 commands =
@@ -116,7 +122,7 @@ commands =
 
 # Release tooling
 [testenv:build]
-basepython = python3
+basepython = python3.5
 skip_install = true
 deps =
     wheel
@@ -125,7 +131,7 @@ commands =
     python setup.py -q sdist bdist_wheel
 
 [testenv:release]
-basepython = python3
+basepython = python3.5
 skip_install = true
 deps =
     {[testenv:build]deps}