diff --git a/django/db/models/base.py b/django/db/models/base.py
index a2f594041e..69224c0287 100644
--- a/django/db/models/base.py
+++ b/django/db/models/base.py
@@ -1100,9 +1100,9 @@ class Model(metaclass=ModelBase):
                         "related object '%s'." % (operation_name, field.name)
                     )
                 elif getattr(self, field.attname) in field.empty_values:
-                    # Use pk from related object if it has been saved after
-                    # an assignment.
-                    setattr(self, field.attname, obj.pk)
+                    # Set related object if it has been saved after an
+                    # assignment.
+                    setattr(self, field.name, obj)
                 # If the relationship's pk/to_field was changed, clear the
                 # cached relationship.
                 if getattr(obj, field.target_field.attname) != getattr(
diff --git a/tests/many_to_one/tests.py b/tests/many_to_one/tests.py
index 2311834481..d9a8984c4c 100644
--- a/tests/many_to_one/tests.py
+++ b/tests/many_to_one/tests.py
@@ -654,6 +654,16 @@ class ManyToOneTests(TestCase):
         self.assertIsNot(c.parent, p)
         self.assertEqual(c.parent, p)
 
+    def test_save_parent_after_assign(self):
+        category = Category(name="cats")
+        record = Record(category=category)
+        category.save()
+        record.save()
+        category.name = "dogs"
+        with self.assertNumQueries(0):
+            self.assertEqual(category.id, record.category_id)
+            self.assertEqual(category.name, record.category.name)
+
     def test_save_nullable_fk_after_parent(self):
         parent = Parent()
         child = ChildNullableParent(parent=parent)