SELECT FOR UPDATE in function

Is't possible to use SELECT FOR UPDATE in functions ?
I have function for 'insert or update' which works ok, but as I have some 
problem with duplicated records I tried as suggested by Tom Lane to use 
SELECT FOR UPDATE instead of just select. Unfortunately it doesn't works:

ERROR:  query didn't return correct # of attributes for *internal*

Here is a function:
CREATE FUNCTION "acc_hits" (int4) RETURNS int4 AS '
Declare   keyval      Alias For $1;   cnt         int4;   curtime     datetime;
Begin   curtime := ''now'';
--    Select count into cnt from hits where msg_id = keyval FOR UPDATE;   Select count into cnt from hits where msg_id = keyval;   if Not Found then       cnt := 1;       -- first_access inserted on default, last_access is NULL       Insert Into hits (msg_id,count) values (keyval, cnt);      else       cnt := cnt + 1;       Update hits set count = cnt,last_access = curtime where msg_id = keyval;   End If;   return cnt;
End;
' LANGUAGE 'plpgsql';

Regards,
	Oleg

PS. 

Just to test:

create table hits (  msg_id int4 not null primary key, count  int4 not null, first_access datetime default now(), last_access datetime   
);   

select acc_hits(1);


_____________________________________________________________
Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
Sternberg Astronomical Institute, Moscow University (Russia)
Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
phone: +007(095)939-16-83, +007(095)939-23-83