diff --git a/guides/source/active_record_migrations.md b/guides/source/active_record_migrations.md
index 5b70bcdb3c..d91c9bd606 100644
--- a/guides/source/active_record_migrations.md
+++ b/guides/source/active_record_migrations.md
@@ -467,6 +467,8 @@ the first time (i.e. on the date the migration is applied).
 Some adapters may support additional options; see the adapter specific API docs
 for further information.
 
+NOTE: `null` and `default` cannot be specified via command line.
+
 ### Foreign Keys
 
 While it's not required you might want to add foreign key constraints to