Fixes #19667.

Change-Id: Iaa71e2020af123c1bd3ac25e0b760956688e8bdf
Reviewed-on: https://go-review.googlesource.com/38458
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>