diff --git a/keystonemiddleware/auth_token.py b/keystonemiddleware/auth_token.py
index 7a078584..07a35827 100644
--- a/keystonemiddleware/auth_token.py
+++ b/keystonemiddleware/auth_token.py
@@ -474,7 +474,7 @@ def _conf_values_type_convert(conf):
     if not conf:
         return {}
     opts = {}
-    opt_types = dict((o.dest, o.type) for o in _OPTS)
+    opt_types = dict((o.dest, getattr(o, 'type', str)) for o in _OPTS)
     for k, v in six.iteritems(conf):
         try:
             if v is None: