For #18130.
Fixes #18655.

Change-Id: I58e2f076b9d8273f128cc033bba9edcd06c81567
Reviewed-on: https://go-review.googlesource.com/35575
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>