Fixes #17439

Change-Id: I7caa28519f38692f9ca306f0789cbb975fa1d7c4
Reviewed-on: https://go-review.googlesource.com/31112Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>