zpbit_in does not receive correct atttypmod

When I create a table

create table test (a bit(4));

and insert a value

insert into test values (b'1000000001');

the zpbit_in() function gets an atttypmod (arg 2 (of 2)) of -1.  Is there
somewhere the system needs to be told that "this type uses the atttypmod
field"?

-- 
Peter Eisentraut   peter_e@gmx.net   http://funkturm.homeip.net/~peter