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