diff --git a/tox.ini b/tox.ini
index 08869bdbd7..fd42389035 100644
--- a/tox.ini
+++ b/tox.ini
@@ -59,7 +59,7 @@ commands =
   python setup.py build_sphinx
 
 [testenv:releasenotes]
-commands = sphinx-build -a -E -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
+commands = sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
 
 [testenv:venv]
 setenv = PYTHONHASHSEED=0