diff --git a/xos/api/utility/modeldefs.py b/xos/api/utility/modeldefs.py
index c3b5e21..a80d677 100644
--- a/xos/api/utility/modeldefs.py
+++ b/xos/api/utility/modeldefs.py
@@ -84,6 +84,8 @@
                     fieldtype = self.convertType(f.get_internal_type())
                     if fieldtype is not None:
                         field['type'] = fieldtype
+                    else:
+                        field['type'] = 'string'
 
                     if not f.blank and not f.null:
                         field['validators']['required'] = True