diff --git a/README.md b/README.md
index 9f739b0..6f45b3a 100644
--- a/README.md
+++ b/README.md
@@ -8,7 +8,7 @@ Guetzli is a Google program to optimize JPEG images. Unfortunately, it only work
 Guetzli must be installed on your system. Follow the official instructions.
 [Guetzli](https://github.com/google/guetzli)
 
-and Python 3.
+and 2.7.10 or Python 3.
 
 # Use