Fixes #19230

Change-Id: I38df9732b88f0328506e74f1a46f52adf47db1e5
Reviewed-on: https://go-review.googlesource.com/38419Reviewed-by: Robert Griesemer <gri@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>