Fixes #16056.

Change-Id: Ic3343914742713851b8ae969b101521f25e85e7b
Reviewed-on: https://go-review.googlesource.com/24132Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>