Fixes #29779

Change-Id: I7eb8b4db187597e07d8ec7d3ff651f008e2ca433
Reviewed-on: https://go-review.googlesource.com/c/158639
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>