ALTER TABLE ( smallinto -> boolean ) ...

I have a table with several 'smallint' fields that I'd like to convert to 
booleean ... the data in each is either 0 or 1, and:

# select '1'::boolean; bool
------ t
(1 row)
# select '0'::boolean; bool
------ f
(1 row)

so they do cast as expected ... but, if I try to do the ALTER, I get:

# ALTER TABLE table ALTER COLUMN field1 type boolean;
ERROR:  column "field1" cannot be cast to type "pg_catalog.bool"

Should this not work?  If not, is there a way to do it so that it will, 
without having to reload the whole table?

Thanks ...

----
Marc G. Fournier           Hub.Org Networking Services (http://www.hub.org)
Email: scrappy@hub.org           Yahoo!: yscrappy              ICQ: 7615664