diff --git a/sql/structure.sql b/sql/structure.sql
index fcf1ca88e5254e45ac4bdfc67b87c7f2532667b1..e83b9bd38869fece662f1e94d4931dbe1fa6cf93 100755
--- a/sql/structure.sql
+++ b/sql/structure.sql
@@ -565,7 +565,7 @@ CREATE TABLE folders
   public boolean NOT NULL,   
   user_id INTEGER NOT NULL,
   parent_id INTEGER,
-  level INTEGER,
+  level INTEGER NOT NULL,
   CONSTRAINT folders_pkey PRIMARY KEY (id)
 )
 WITH (OIDS=FALSE);