This came up in private mail.
It works today and I want to make sure it stays working.

Change-Id: I13ebdc2dfadb3c72d7f179be89883137320c05d0
Reviewed-on: https://go-review.googlesource.com/7390Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Rob Pike <r@golang.org>