diff --git a/awx/main/utils/polymorphic.py b/awx/main/utils/polymorphic.py
index 28f8a11187..a821ffeb10 100644
--- a/awx/main/utils/polymorphic.py
+++ b/awx/main/utils/polymorphic.py
@@ -15,4 +15,6 @@ def build_polymorphic_ctypes_map(cls):
 
 
 def SET_NULL(collector, field, sub_objs, using):
-    return models.SET_NULL(collector, field, sub_objs.non_polymorphic(), using)
+    if hasattr(sub_objs, 'non_polymorphic'):
+        sub_objs = sub_objs.non_polymorphic()
+    return models.SET_NULL(collector, field, sub_objs, using)