Fixes #20090

Change-Id: I881607e55cd946a703e74a7d8ae2bbde67546510
Reviewed-on: https://go-review.googlesource.com/45816Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>