diff --git a/requirements.txt b/requirements.txt
index 60dee97..be825f0 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -2,6 +2,7 @@
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
 pbr<2.0,>=0.11
+cliff>=1.13.0 # Apache-2.0
 anyjson>=0.3.3
 httplib2>=0.7.5
 jsonschema!=2.5.0,<3.0.0,>=2.0.0