How to use Scala 2.10 implicit classes

I thought this would be correct usage of the new implicit classes of Scala 2.10:

implicit case class IntOps(i: Int) extends AnyVal {
  def twice = i * 2
}

11.twice

Apparently not:

<console>:13: error: value twice is not a member of Int
              11.twice
                 ^

Am I missing something (Scala 2.10.0-M6)?