Fixes #15109.

Change-Id: Ibfdedd6807322ebec84bacfeb492fb53fe066960
Reviewed-on: https://go-review.googlesource.com/23742
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>