Fixes #13993

Change-Id: Ic61b2bcd9f4f71457d3a8581574633d505d5750e
Reviewed-on: https://go-review.googlesource.com/27240
Run-TryBot: Rob Pike <r@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>