return query and function result type must be real because of OUT parameters

I was doing some test to track down an error in a more
complicated function and I stumbled in this behaviour I can't
understand:

create or replace function test.test(out _rank float4) returns setof
record as $$
begin
return query select 1::float4;
return;
end;
$$ language plpgsql stable;

and I get

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


********** Error **********

ERROR: function result type must be real because of OUT parameters
SQL state: 42P13

same with text etc...

--
Ivan Sergio Borgonovo
http://www.webthatworks.it