diff --git a/tox.ini b/tox.ini
index 8f53699..d7fcf86 100644
--- a/tox.ini
+++ b/tox.ini
@@ -17,6 +17,6 @@ commands = {posargs}
 
 [testenv:docs]
 commands =
-    sphinx-build -b html doc/source/ doc/build/html
-    sphinx-build -b latex doc/source/ doc/build/latex
-    sphinx-build -b pdf doc/source/ doc/build/pdf
+    sphinx-build -b html -W doc/source/ doc/build/html
+    sphinx-build -b latex -W doc/source/ doc/build/latex
+    sphinx-build -b pdf -W doc/source/ doc/build/pdf