Fixes #8859

Change-Id: If8098e6edad1f83dc35fa84f4431689e8ee97678
Reviewed-on: https://go-review.googlesource.com/6701Reviewed-by: Rob Pike <r@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>