diff --git a/sql/mysql/upgrade/3.5.0/folder_descendants.sql b/sql/mysql/upgrade/3.5.0/folder_descendants.sql
index dd3e294..4fb4a8d 100755
--- a/sql/mysql/upgrade/3.5.0/folder_descendants.sql
+++ b/sql/mysql/upgrade/3.5.0/folder_descendants.sql
@@ -3,4 +3,7 @@ CREATE TABLE `folder_descendants`
 	`parent_id` int(11) NOT NULL,
     `folder_id` int(11) NOT NULL,
     primary key (parent_id,folder_id)
-) ENGINE=InnoDB DEFAULT CHARSET=utf8;
\ No newline at end of file
+) ENGINE=InnoDB DEFAULT CHARSET=utf8;
+
+alter table folder_descendants add foreign key(parent_id) references folders(id);
+alter table folder_descendants add foreign key(folder_id) references folders(id);
\ No newline at end of file