Appease vet.

Change-Id: Ie88de08b91041990c0eaf2e15628cdb98d40c660
Reviewed-on: https://go-review.googlesource.com/36938
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>