Follow-up on https://golang.org/cl/143037.

Change-Id: Ia36760b499f7d46ce03e0fa81ec455a4a20208ac
Reviewed-on: https://go-review.googlesource.com/c/143061
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>