diff --git a/requirements.txt b/requirements.txt
index b257d7b..0a91aa0 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,3 +1,3 @@
-six>=1.7.0
+six>=1.9.0
 futures>=3.0;python_version=='2.7'
 monotonic>=0.6 # Apache-2.0