array_agg problem

array_agg says it can take any type of arg, but this seems not to work
when the arg in an integer array.

create temp table x(name text, val integer[]);
insert into x values('a',array[1,2,3]);
insert into x values('b',array[3,4,5]);
select * from x;
select max(val), min(val) from x;
select array_agg(val) from x;

Well, everything works except the last statement. In 8.4 I get
ERROR: could not find array type for data type integer[]

I was hoping for [1,2,3,4,5] or at least [1,2,3,3,4,5] or even [[1,2,3],[3,4,5]]
Am I not understanding something?

Thanks,
TJ O'Donnell