implicit tables syntax disappeared from 8.0->8.1

Hello,

the following used to work:

create table t1(t1f1 text, t1f2 text, t1f3 text);
create table t2(t2f2 text, t2f3 text);

insert ...

update   t1
set  t1f1='test'
where  t1.t1f2=t2.t2f2
and  t1.t1f3=t2.t2f3;

unfortunately, now I get the error that t2 is not in the FROM clause.

I know I can do

update t1
set t1f1='test'
where t1.t1f2||'/'||t1.t1f3 in
(select t2.t2f2||'/'||t2.t2f3 from t2);

But I'm afraid that's very expensive.  Do you have a suggestion for
alternative syntax for my initial query?

Thank you,

Oliver Seidel