Fixes #21435

Change-Id: I5f8d93a45b84a871ceea881ecb1a38a37e96006c
Reviewed-on: https://go-review.googlesource.com/55263Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>