Fixes #11552

Change-Id: I87904e9e3fb4bd1fb4c7075a4e2d0151e5bd37df
Reviewed-on: https://go-review.googlesource.com/11890
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Mikio Hara <mikioh.mikioh@gmail.com>
Reviewed-by: David Crawshaw <crawshaw@golang.org>