Fixes #17040

Change-Id: I3682cc0367b919084c280d7dc64746495c1d4aaa
Reviewed-on: https://go-review.googlesource.com/28872Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>