Required to pass the issue9400 test.

Change-Id: I595223c403b12faade54e2e46510f8537150af39
Reviewed-on: https://go-review.googlesource.com/20940Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>