Fixes #14493
Updates #6458 (changes its behavior)

Change-Id: I851a8113fd312dae3384e989ec2b70949dc22838
Reviewed-on: https://go-review.googlesource.com/21811
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Quentin Smith <quentin@golang.org>