Fixes #14432.

Change-Id: I0a92ef86de95de39217df9a664d8034ef685a906
Reviewed-on: https://go-review.googlesource.com/19792Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Minux Ma <minux@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>