diff --git a/tox.ini b/tox.ini
index d8cb508..bee979a 100644
--- a/tox.ini
+++ b/tox.ini
@@ -18,7 +18,7 @@ commands = {posargs}
 deps =
   -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt}
   -r{toxinidir}/doc/requirements.tx
-commands = sphinx-build -b html doc/source doc/build/html
+commands = sphinx-build -W -b html doc/source doc/build/html
 
 [testenv:spelling]
 deps =