Fixes #15355

Change-Id: Idbab7a627c5de249bb62d519c5a47f3d2f6c82a7
Reviewed-on: https://go-review.googlesource.com/22796Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>