Error using first_value/last_value window function with aggregated function

create table t1 (a int);

insert into t1 values (1), (2), (3);

select  first_value(avg(a)) over () from t1;

MariaDB [test]> select  first_value(avg(a)) over () from t1;

ERROR 1111 (HY000): Invalid use of group function

mysql> select  first_value(avg(a)) over () from t1;

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

| first_value(avg(a)) over () |

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

|                      2.0000 |

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

1 row in set (0.00 sec)