diff --git a/watcher/api/middleware/auth_token.py b/watcher/api/middleware/auth_token.py
index 942bc5a0e..585d4958e 100644
--- a/watcher/api/middleware/auth_token.py
+++ b/watcher/api/middleware/auth_token.py
@@ -33,7 +33,7 @@ class AuthTokenMiddleware(auth_token.AuthProtocol):
     for public routes in the API.
 
     """
-    def __init__(self, app, conf, public_api_routes=[]):
+    def __init__(self, app, conf, public_api_routes=()):
         route_pattern_tpl = '%s(\.json|\.xml)?$'
 
         try: