diff --git a/requirements.txt b/requirements.txt
index ed129b2ce..1a34ed606 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -3,5 +3,6 @@
 # process, which may cause wedges in the gate later.
 pbr>=0.6,!=0.7,<1.0
 requests>=2.2.0,!=2.4.0
+six>=1.7.0
 stevedore>=1.1.0  # Apache-2.0
 oslo.utils>=1.2.0                       # Apache-2.0