Fixes golang/go#16137

Change-Id: I0b7ebb71b95de3c262242ddb4032da5f470f5643
Reviewed-on: https://go-review.googlesource.com/80535
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>