Fixes #21414

Change-Id: I8b25d416e6ead087b4a9965e8fa1a7f59ff07291
Reviewed-on: https://go-review.googlesource.com/59290Reviewed-by: Hiroshi Ioka <hirochachacha@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>