Fixes #12674

Change-Id: I82f53026dd2fc27bd7999d43c27932d683d92af6
Reviewed-on: https://go-review.googlesource.com/15730Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>