diff --git a/db/routines/vn/procedures/entry_checkBooked.sql b/db/routines/vn/procedures/entry_checkBooked.sql
index 3ca8c9642..7ee1fee22 100644
--- a/db/routines/vn/procedures/entry_checkBooked.sql
+++ b/db/routines/vn/procedures/entry_checkBooked.sql
@@ -15,7 +15,7 @@ BEGIN
 		FROM `entry`
 		WHERE id = vSelf;
 
-	IF vIsBooked AND NOT @isModeInventory THEN
+	IF vIsBooked AND NOT IFNULL(@isModeInventory, FALSE) THEN
 		CALL util.throw('Entry is already booked');
 	END IF;
 END$$