Fixes the build.

Updates #18199

Change-Id: Ibf029ba9f9293d1f3d49c1c8773fc262159a5d5b
Reviewed-on: https://go-review.googlesource.com/34242Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>