Fixes #18494

Change-Id: I8a190acae6d5f1d20d4e4e4547d84e10e8a7fe68
Reviewed-on: https://go-review.googlesource.com/34793Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>