diff --git a/categories/registration.py b/categories/registration.py
index 3ba34b7..a4d6eb1 100644
--- a/categories/registration.py
+++ b/categories/registration.py
@@ -62,7 +62,7 @@ class Registry(object):
         for fld in field_definitions:
             extra_params = {'to': 'categories.Category', 'blank': True}
             if field_type != 'ManyToManyField':
-                extra_params['on_delete'] = 'CASCADE'
+                extra_params['on_delete'] = CASCADE
                 extra_params['null'] = True
             if isinstance(fld, str):
                 field_name = fld