MySQL и триггеры

DELIMITER $$
CREATE TRIGGER a_after_insert
AFTER INSERT ON a FOR EACH ROW BEGIN
  INSERT INTO b (a_id) VALUES (NEW.id);
END$$
DELIMITER ;

DELIMITER $$
CREATE TRIGGER b_after_insert
AFTER INSERT ON b FOR EACH ROW BEGIN
  UPDATE a SET b_id = NEW.id WHERE id = NEW.a_id;
END$$
DELIMITER ;

ERROR 1442 (HY000): Can't update table 'a' in stored function/trigger because it is already used by statement which invoked this stored function/trigger.