Fixes #16021.

Change-Id: I55df38bbccd2641abcb54704115002a9aa04325d
Reviewed-on: https://go-review.googlesource.com/23962
Run-TryBot: Michael Munday <munday@ca.ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>