Fixes golang/go#17868

Change-Id: I7f9d85f404198d68757d7ca5bb8b1e7aafaafa8b
Reviewed-on: https://go-review.googlesource.com/33013
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Tom Bergan <tombergan@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>