diff --git a/tox.ini b/tox.ini
index 9bd70269..9f71ed25 100644
--- a/tox.ini
+++ b/tox.ini
@@ -52,6 +52,7 @@ commands =
 deps =
     sphinx
     sphinx_rtd_theme
+    sphinx-notfound-page
     restructuredtext-lint
 commands =
     sphinx-build -W -b html -d {envtmpdir}/doctrees docs docs/_build/html