Casting int to bool with join...

I am trying to update rows in a new table and re-cast to boolean at the 
same time.  I am absolutely certain that the integers are 0 or 1.  Is 
there a one line way to do this?

UPDATE app_id_800 SET cal_byte_w_err = cal_byte_w_err.value::boolean
FROM cal_byte_w_err
WHERE app_id_800.timestamp BETWEEN '2004-01-01 00:00:00' AND 
'2004-01-01 00:00:05'
AND app_id_800.timestamp = cal_byte_w_err.timestamp;

Many thanks... I've spent way too long trying to figure this out :(

Cheers,
Randall