diff --git a/tox.ini b/tox.ini
index 3d5f89d..780c7d4 100644
--- a/tox.ini
+++ b/tox.ini
@@ -69,8 +69,11 @@ commands=
     python setup.py build_sphinx
 
 [flake8]
+# [H106] Don't put vim configuration in source files.
+# [H203] Use assertIs(Not)None to check for None.
 show-source = True
 exclude=.venv,.git,.tox,dist,doc,*lib/python*,*egg,build,releasenotes
+enable-extensions = H106,H203
 
 [testenv:releasenotes]
 commands = sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html