Fixes #15148.

Change-Id: If3b628f30521adeec1625689dbc98aaf4a9ec858
Reviewed-on: https://go-review.googlesource.com/22811Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Minux Ma <minux@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>