Fixes #16736

Change-Id: I335d201e3f6738d838de3881087cb640fc7670e8
Reviewed-on: https://go-review.googlesource.com/30578
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>