Fixes #13705

Change-Id: I86c60c78ce0394f830f904c9cba83ebbf3efc046
Reviewed-on: https://go-review.googlesource.com/21328
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>