Fixes: golang/go#21410

Change-Id: Ie1971f7d6e0cfe405603e94c538a15dd5f467392
Reviewed-on: https://go-review.googlesource.com/55230
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>