serial arrays?

A recent message from a would-be mysql converter led me to realize
that we don't check for array decoration when we expand "serial".
So this is accepted but doesn't do what one might expect:

regression=# create table foo (f1 serial[11]);
NOTICE:  CREATE TABLE will create implicit sequence "foo_f1_seq" for serial column "foo.f1"
CREATE TABLE
regression=# \d foo                        Table "public.foo"Column |  Type   |                    Modifiers
        
 
--------+---------+--------------------------------------------------f1     | integer | not null default
nextval('foo_f1_seq'::regclass)


Should we throw an error for this?  If not, what behavior would be
sane?
        regards, tom lane