This part got dropped when we were debating between two solutions
in https://golang.org/cl/15151

Fixes #13032

Change-Id: I820b94f6c0c102ccf9342abf957328ea01f49a26
Reviewed-on: https://go-review.googlesource.com/16313Reviewed-by: Austin Clements <austin@google.com>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>