diff --git a/setup.cfg b/setup.cfg
index bf219e9..f64a17d 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -26,6 +26,7 @@ packages =
 source-dir = doc/source
 build-dir = doc/build
 all_files = 1
+warning-is-error = 1
 
 [upload_sphinx]
 upload-dir = doc/build/html
diff --git a/tox.ini b/tox.ini
index cda97a3..9e73812 100644
--- a/tox.ini
+++ b/tox.ini
@@ -33,7 +33,7 @@ commands =
   coverage report
 
 [testenv:docs]
-commands = sphinx-build -W -b html doc/source doc/build/html
+commands = python setup.py build_sphinx
 
 [testenv:api-ref]
 whitelist_externals = rm