diff --git a/tox.ini b/tox.ini
index 62643da..6db663f 100644
--- a/tox.ini
+++ b/tox.ini
@@ -28,7 +28,8 @@ commands = {posargs}
 
 [testenv:docs]
 basepython = python3
-commands = python setup.py build_sphinx
+commands =
+  sphinx-build -W -b html doc/source doc/build/html
 
 
 [testenv:lower-constraints]