Fixes #22599.

Change-Id: I2d59a8fae457881f681184fc6ed1f2aa597699b3
Reviewed-on: https://go-review.googlesource.com/76026
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>