Fixes #17270.

Change-Id: I4affa57e10baf1a758bc0977265d160f220b2945
Reviewed-on: https://go-review.googlesource.com/29960
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>