Fixes #15647

Change-Id: I588bfa4eb336d1da1fcda8d06e32ed13c0b51c70
Reviewed-on: https://go-review.googlesource.com/23061
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>