Fixes #15884

Change-Id: I33d98db861d74e3c37a546efaf83ce6f2f76d335
Reviewed-on: https://go-review.googlesource.com/24391
Run-TryBot: Rob Pike <r@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>