diff --git a/tox.ini b/tox.ini
index 8d0ae601..482ead88 100644
--- a/tox.ini
+++ b/tox.ini
@@ -46,7 +46,7 @@ setenv = VIRTUAL_ENV={envdir}
 commands = bash tools/lintstack.sh
 
 [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
 
 [flake8]
 show-source = true