diff --git a/requirements.txt b/requirements.txt
index 2e39e22286..e0d7ab4b3d 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -25,7 +25,7 @@ ipython
 html2text
 email_reply_parser
 click
-num2words
+num2words==0.5.4
 watchdog==0.8.0
 bleach
 bleach-whitelist