diff --git a/tox.ini b/tox.ini
index 6d68f28..228c3fe 100644
--- a/tox.ini
+++ b/tox.ini
@@ -66,7 +66,7 @@ commands = sphinx-build -W -b html doc/source doc/build/html
 [testenv:docs-constraints]
 basepython = python3
 install_command = {[testenv:common-constraints]install_command}
-commands = python setup.py build_sphinx
+commands = sphinx-build -W -b html doc/source doc/build/html
 
 [testenv:debug]
 basepython = python3