Fixes #17232

Change-Id: I34df86f79b643dce9f054c6df6782e6037c06910
Reviewed-on: https://go-review.googlesource.com/30158
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>