diff --git a/requirements.txt b/requirements.txt
index 9d002744495..a1cc88cfe73 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -3,3 +3,4 @@ enum34>=1.0.4
 futures>=2.2.0
 cython>=0.23
 coverage>=4.0
+six>=1.10