Cannot use nextval() inside trigger

MariaDB [test]> create or replace trigger ti before insert on a for each row set new.a=nexval(aseq);

Query OK, 0 rows affected (0.07 sec)

MariaDB [test]> select nextval(aseq);

+---------------+

| nextval(aseq) |

+---------------+

|           133 |

+---------------+

1 row in set (0.00 sec)

MariaDB [test]> insert into a select null;

ERROR 1305 (42000): FUNCTION test.nexval does not exist

MariaDB [test]> show create table a\G

*************************** 1. row ***************************

       Table: a

Create Table: CREATE TABLE `a` (

  `a` int(11) DEFAULT NULL

) ENGINE=InnoDB DEFAULT CHARSET=latin1

1 row in set (0.00 sec)

MariaDB [test]> create procedure d() select nextval(aseq);

Query OK, 0 rows affected (0.01 sec)

MariaDB [test]> call d;

+---------------+

| nextval(aseq) |

+---------------+

|           134 |

+---------------+

1 row in set (0.00 sec)

Query OK, 0 rows affected (0.00 sec)