diff --git a/docs/releases/1.6.3.txt b/docs/releases/1.6.3.txt
index 99b8566270e..a8b63dc72ae 100644
--- a/docs/releases/1.6.3.txt
+++ b/docs/releases/1.6.3.txt
@@ -14,3 +14,7 @@ several bugs in 1.6.2:
 * Fixed ``AttributeError`` when using
   :meth:`~django.db.models.query.QuerySet.bulk_create` with ``ForeignObject``
   (`#21566 <http://code.djangoproject.com/ticket/21566>`_).
+
+* Fixed crash of ``QuerySet``\s that use ``F() + timedelta()`` when their query
+  was compiled more once
+  (`#21643 <http://code.djangoproject.com/ticket/21643>`_).
diff --git a/tests/expressions_regress/tests.py b/tests/expressions_regress/tests.py
index 7533e4ee39a..8f87940c9e2 100644
--- a/tests/expressions_regress/tests.py
+++ b/tests/expressions_regress/tests.py
@@ -281,6 +281,13 @@ class FTimeDeltaTests(TestCase):
         q2 = str(queryset.query)
         self.assertEqual(q1, q2)
 
+    def test_query_clone(self):
+        # Ticket #21643
+        qs = Experiment.objects.filter(end__lt=F('start') + datetime.timedelta(hours=1))
+        qs2 = qs.all()
+        list(qs)
+        list(qs2)
+
     def test_delta_add(self):
         for i in range(len(self.deltas)):
             delta = self.deltas[i]