Fixes #16690

Change-Id: I6db588c4b0f23c5ec6bc9b85a488b60fab3f2f13
Reviewed-on: https://go-review.googlesource.com/30892Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>