"The tuple structure of a not-yet-assigned record is indeterminate."

In my function I have (kept the important part)

CREATE OR REPLACE FUNCTION foo() RETURNS SETOF RECORD AS $$
DECLARE
retval RECORD;
BEGIN
some loop
retval.jd := tmp.id;
retval.d2 := _c2;
retval.d3 := _c3;
RETURN NEXT retval;
end loop
return;
END;

and I get

ERROR: record "retval" is not assigned yet
DETAIL: The tuple structure of a not-yet-assigned record is indeterminate.
CONTEXT: PL/pgSQL function "foo" line 33 at assignment

It seems that the line with retval.jd := tmp.id; is where it stops.
Any suggestion on how to fix this error?