Fixes golang/go#19125

Change-Id: I822b6f260f980178da29a552c6170cb261c8e254
Reviewed-on: https://go-review.googlesource.com/37152
Run-TryBot: Matt Layher <mdlayher@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>