fixes #21619

Change-Id: I5bb513dfc8cac875b06a262eec40b5863ae23a4c
Reviewed-on: https://go-review.googlesource.com/62370Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>