Fixes #21950

Change-Id: I6fa392abd2c3bf6a4f80f14c6b1419470e9a944d
Reviewed-on: https://go-review.googlesource.com/66750
Run-TryBot: Rob Pike <r@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>