diff --git a/tox.ini b/tox.ini
index 3192ca77d..5a1ffc226 100644
--- a/tox.ini
+++ b/tox.ini
@@ -75,10 +75,7 @@ envdir = {toxworkdir}/venv
 commands =
     oslo-config-generator --config-file etc/zun/zun-config-generator.conf
 
-# we do not used -W here because we are doing some slightly tricky
-# things to build a single page document, and as such, we are ok
-# ignoring the duplicate stanzas warning.
 [testenv:api-ref]
 commands =
   rm -rf api-ref/build
-  sphinx-build -b html -d api-ref/build/doctrees api-ref/source api-ref/build/html
+  sphinx-build -W -b html -d api-ref/build/doctrees api-ref/source api-ref/build/html