diff --git a/tox.ini b/tox.ini
index 2077703..f59cd5d 100644
--- a/tox.ini
+++ b/tox.ini
@@ -34,7 +34,7 @@ setenv =
 
 [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
 commands=
     bash -c "rm -rf doc/build"