Fixes build.

Change-Id: Idd7d87f0bf3fe553b3ab00dd32eee4925a4fe3ff
Reviewed-on: https://go-review.googlesource.com/18647
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>