diff --git a/refstack/tests/unit/test_app.py b/refstack/tests/unit/test_app.py
index 5e089f2c..aebd41f8 100644
--- a/refstack/tests/unit/test_app.py
+++ b/refstack/tests/unit/test_app.py
@@ -94,7 +94,7 @@ class JSONErrorHookTestCase(base.BaseTestCase):
         exc = mock.Mock(spec=webob.exc.HTTPRedirection)
         hook = app.JSONErrorHook()
         result = hook.on_error(mock.Mock(), exc)
-        self.assertEqual(result, None)
+        self.assertIsNone(result)
 
     @mock.patch.object(webob, 'Response')
     def test_on_error_with_other_exceptions(self, response):
diff --git a/tox.ini b/tox.ini
index 2c423eea..134d6191 100644
--- a/tox.ini
+++ b/tox.ini
@@ -70,6 +70,7 @@ commands = python setup.py build_sphinx {posargs}
 # E125 continuation line does not distinguish itself from next logical line
 # H404 multi line docstring should start with a summary
 ignore = E125,H404
+enable-extensions = H203
 show-source = true
 builtins = _
 exclude=.venv,.git,.tox,dist,doc,*lib/python*,*egg,tools,build