8.3 PLpgSQL Can't Compare Records?

This code:

CREATE OR REPLACE FUNCTION foo() returns boolean as $$
DECLARE
have_rec record;
want_rec record;
BEGIN
have_rec := row(1, 2);
want_rec := row(3, 5);
RETURN have_rec IS DISTINCT FROM want_rec;
END;
$$ language plpgsql;

SELECT ROW(1, 2) IS DISTINCT FROM ROW(3, 5);

SELECT foo();
DROP FUNCTION foo();

Works as expected on 8.4, outputting:

?column?
----------
t
(1 row)

Time: 48.626 ms
foo
-----
t
(1 row)

On 8.3, however, the row comparisons in the SQL statement works, but
fails in the PL/pgSQL function, with this output:

?column?
----------
t
(1 row)

psql:huh.sql:14: ERROR: operator does not exist: record = record
LINE 1: SELECT $1 IS DISTINCT FROM $2
^
HINT: No operator matches the given name and argument type(s).
You might need to add explicit type casts.
QUERY: SELECT $1 IS DISTINCT FROM $2
CONTEXT: PL/pgSQL function "foo" line 7 at RETURN

Is this a known issue in 8.3? If so, is there a known workaround?

Thanks,

David