Fixes #21800

Change-Id: I6c61d3543f28e9951b2a219b3c7298077b38f29e
Reviewed-on: https://go-review.googlesource.com/66210
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>