Fixes #20325

Change-Id: Ie363fef73d0deae40af41ee3f4403ad18546eba6
Reviewed-on: https://go-review.googlesource.com/43460
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>