diff --git a/util/http.py b/util/http.py
index 26451e9dc..dd1df29d8 100644
--- a/util/http.py
+++ b/util/http.py
@@ -11,7 +11,7 @@ DEFAULT_MESSAGE[403] = 'Permission Denied'
 DEFAULT_MESSAGE[404] = 'Not Found'
 
 def abort(status_code, message=None, **kwargs):
-  message = message % kwargs if message else DEFAULT_MESSAGE[status_code] 
+  message = str(message) % kwargs if message else DEFAULT_MESSAGE[status_code] 
 
   if status_code == 403:
     # Add the user information.