diff --git a/tox.ini b/tox.ini
index 5face04d8..82195f8ff 100644
--- a/tox.ini
+++ b/tox.ini
@@ -23,7 +23,7 @@ commands = {posargs}
 
 [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 =
   /bin/rm -fr doc/build/