Fixes #8973

Change-Id: I746fae430db6d8f9ebd33586b8cffcb31d688cc8
Reviewed-on: https://go-review.googlesource.com/10284
Run-TryBot: Minux Ma <minux@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>