Fixes #11207

Change-Id: I7f00b638e749fbc7907dc1597347ea426367d13e
Reviewed-on: https://go-review.googlesource.com/17980
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>