Fixes #9039.

Change-Id: I7d213b4f8e4cda73ea7687fb97dbd22e58163949
Reviewed-on: https://go-review.googlesource.com/9683
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>