Array of Arrays of int

Why does

select array(select array[1,2]);

give me an error: "could not find array type for data type integer[]"?

Is there a type-cast missing, or is this generally impossible? I was
expecting something like

{{1,2}}

In my real-world application, the subquery returns more than one pair
of ints, but I think it all boils down to this simpler example. I am
using version 7.4 of PostgreSQL.

Thanks a lot,
Leo