query on smallint array column

Hi,
I was experimenting with the following query.

create table sint1(k int primary key, arr smallint[]);
create index s1 on sint1(arr);
insert into sint1 select s, array[s*s, s] FROM generate_series(1, 10) AS s;
select * from sint1 where arr @> array[4];
ERROR: operator does not exist: smallint[] @> integer[]
LINE 1: select * from sint1 where arr @> array[4];
^
HINT: No operator matches the given name and argument types. You might
need to add explicit type casts.
-------

I wonder if someone can enlighten me on the correct way to perform the type
cast.

Thanks