Fixes #20636

Change-Id: Icea0012fecb73944c95f6037922505c63b57b245
Reviewed-on: https://go-review.googlesource.com/45295Reviewed-by: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>