why aren't these returning unique?

gistfile1.rb

ruby-1.9.2-p290 :056 > Sermon.where("date > ?", Date.today - 365).select(:speaker_id).uniq
  Sermon Load (0.5ms)  SELECT speaker_id FROM "sermons" WHERE (date > '2011-02-07')
 => [#<Sermon speaker_id: 1>, #<Sermon speaker_id: 1>, #<Sermon speaker_id: 1>, #<Sermon speaker_id: 1>, #<Sermon speaker_id: 1>] 

Update: answer:

ruby-1.9.2-p290 :070 > Sermon.select(:speaker_id).where("date > ?", Date.today - 365).group(:speaker_id)
  Sermon Load (0.5ms)  SELECT speaker_id FROM "sermons" WHERE (date > '2011-02-07') GROUP BY speaker_id
 => [#<Sermon speaker_id: 1>]