diff --git a/docs/ref/models/fields.txt b/docs/ref/models/fields.txt
index c7e7eb928c..bb2f7fff59 100644
--- a/docs/ref/models/fields.txt
+++ b/docs/ref/models/fields.txt
@@ -1271,6 +1271,9 @@ relation works.
             null=True,
         )
 
+    ``on_delete`` doesn't create a SQL constraint in the database. Support for
+    database-level cascade options :ticket:`may be implemented later <21961>`.
+
 The possible values for :attr:`~ForeignKey.on_delete` are found in
 :mod:`django.db.models`: