Fixes #14300.

Change-Id: Idb6a300fe0e06fb8966cf06b55f9b252752a69a6
Reviewed-on: https://go-review.googlesource.com/19459Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Michael Hudson-Doyle <michael.hudson@canonical.com>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>