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