Fixes #20239

Change-Id: Icb021daad82e6905f536e4ef09ab219500b08167
Reviewed-on: https://go-review.googlesource.com/81778
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>