Fixes #14164.

Change-Id: Ib1d1d29674c99cf88e0ae12724823a31f5dbb95c
Reviewed-on: https://go-review.googlesource.com/19087
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>