Fixes golang/go#24137

Change-Id: Ifcf6449aed32071cdb643028347ec814bffd8d06
Reviewed-on: https://go-review.googlesource.com/127121Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>