diff --git a/util/config/validator.py b/util/config/validator.py
index 1fda3e911..6a09a1609 100644
--- a/util/config/validator.py
+++ b/util/config/validator.py
@@ -331,8 +331,8 @@ def _validate_jwt(config):
   username = get_authenticated_user().username
   result = users.user_exists(username)
   if not result:
-    raise Exception('Verification of superuser %s failed. The user either does not exist ' +
-                    'in the remote authentication system OR JWT auth is misconfigured.' % username)
+    raise Exception(('Verification of superuser %s failed. The user either does not exist ' +
+                     'in the remote authentication system OR JWT auth is misconfigured.') % username)
 
 
 _VALIDATORS = {