[racket] has contract-out been renamed?

DrRacket version 5.1.3:

file contents:

#lang racket
(provide (contract-out (x integer?)))
(define x 3)

run result:

contract-out: not a provide sub-form in: (contract-out (x integer?))

Do I need to upgrade to 5.2?

(I'm following the documentation at
http://docs.racket-lang.org/guide/contract-boundaries.html.)

Thanks!

--Dan