Fixes #16712.

Change-Id: Ib216059c6c0c952162c19e080dcf3799f0652a8d
Reviewed-on: https://go-review.googlesource.com/32171
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Quentin Smith <quentin@golang.org>