diff --git a/activerecord/lib/active_record/migration.rb b/activerecord/lib/active_record/migration.rb
index 9b93366906..90984b080b 100644
--- a/activerecord/lib/active_record/migration.rb
+++ b/activerecord/lib/active_record/migration.rb
@@ -92,6 +92,7 @@ module ActiveRecord
   #   
   #     def self.down
   #       # not much we can do to restore deleted data
+  #       raise IrreversibleMigration
   #     end
   #   end
   #