diff --git a/tox.ini b/tox.ini
index 2172188..01e6831 100644
--- a/tox.ini
+++ b/tox.ini
@@ -44,7 +44,7 @@ commands =
 
 [testenv:docs]
 deps =
-  -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+  -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
   -r{toxinidir}/doc/requirements.txt
 whitelist_externals = rm
 commands =