Fixes #15316.
Fixes #15574.

Change-Id: I3ec8bffd35b9e5123de4be983a53fc0b8c2a0895
Reviewed-on: https://go-review.googlesource.com/23242
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>