Fixes #13610

Change-Id: I9c8f924dc1ad515a9697291e981ece34fdbec8b7
Reviewed-on: https://go-review.googlesource.com/17755
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>