Cast Const Integer to Bigint in Postgres

I'm getting the below error while running the below script. My goal is to create a function in Postgres to return 1 as a bigint. Help please!

hashtagpostgresnoobie

ERROR: function result type must be bigint because of OUT parameters

CREATE OR REPLACE FUNCTION GetNumberOne(
    OUT numberone bigint)
  RETURNS SETOF record AS
$BODY$

    SELECT CAST(1 AS BIGINT) AS "NUMBERONE";

$BODY$
  LANGUAGE sql VOLATILE;