constraints on composite types

This fails on 8.0.3 (syntax error at or near "." at character):

CREATE TYPE ct AS (
  foo INTEGER,
  bar INTEGER
);

CREATE TABLE t1 (
  attr ct,
  CONSTRAINT uq UNIQUE (attr.foo)
);

Should it be possible? From reading
http://www.postgresql.org/docs/current/static/rowtypes.html it looks
like almost everything else works.

--
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