diff --git a/appengine/flexible/twilio/requirements.txt b/appengine/flexible/twilio/requirements.txt
index 306db876c75..dda690ab2e6 100644
--- a/appengine/flexible/twilio/requirements.txt
+++ b/appengine/flexible/twilio/requirements.txt
@@ -1,3 +1,3 @@
 Flask==0.12.2
 gunicorn==19.7.1
-twilio==6.3.dev0
+twilio<=6.0.0dev,==5.4.0