diff --git a/tox.ini b/tox.ini
index 3ad9c559..9f2694ff 100644
--- a/tox.ini
+++ b/tox.ini
@@ -32,8 +32,10 @@ commands = {posargs}
 commands = python setup.py test --coverage --coverage-package-name=translator --testr-args='{posargs}'
 
 [testenv:docs]
-deps = -r{toxinidir}/doc/requirements.txt
-commands = sphinx-build -b html doc/source doc/build/html
+deps =
+  -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+  -r{toxinidir}/doc/requirements.txt
+commands = sphinx-build -W -b html doc/source doc/build/html
 
 [testenv:debug]
 commands =