Fixes #19832

Change-Id: I7ce39c2c435d4716d8a42ac6784b4c87874c0e13
Reviewed-on: https://go-review.googlesource.com/49490
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>