diff --git a/django/db/models/base.py b/django/db/models/base.py
index 5dd11a9d832d1..3b6a5fe1ea86d 100644
--- a/django/db/models/base.py
+++ b/django/db/models/base.py
@@ -378,7 +378,7 @@ def _collect_sub_objects(self, seen_objs):
         pk_val = self._get_pk_val()
         if pk_val in seen_objs.setdefault(self.__class__, {}):
             return
-        seen_objs.setdefault(self.__class__, {})[pk_val] = self
+        seen_objs[self.__class__][pk_val] = self
 
         for related in self._meta.get_all_related_objects():
             rel_opts_name = related.get_accessor_name()