Fixes #16732

Change-Id: If0a7f9425cf75b9e31b3091c43cb23d6e039f568
Reviewed-on: https://go-review.googlesource.com/28782
TryBot-Result: Gobot Gobot <gobot@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>