diff --git a/tests/queryset/transform.py b/tests/queryset/transform.py
index a2636122..a1f060d5 100644
--- a/tests/queryset/transform.py
+++ b/tests/queryset/transform.py
@@ -1,5 +1,7 @@
 import unittest
 
+from bson.son import SON
+
 from mongoengine import *
 from mongoengine.queryset import Q, transform