Trouble with UEFI installation

[andrew . erlanger]

Hello again, Guix users.

I'm still trying to install GuixSD, and my problem is with UEFI. I've
got Gentoo working with UEFI, so I know it's possible on this machine.

The problem occurs in the installation. This is my error:

> copying '/gnu/store/1ajp6plak42nr93kyprmc3c4gf6fjvxq-grub.cfg'...
> populating '/mnt'...
> grub-install: error: 
> /gnu/store/ipwgwqaarp304r82b97748shwzmwa9k0-grub-efi-2.02/lib/grub/i386-pc/modinfo.sh
>  doesn't exist. Please specify --target or --directory.
> guix system: error: failed to install GRUB on device '/dev/sda'

So grub isn't being passed --target=x86_64-efi. And I don't know how to
pass the argument manually. My config is as below:

> (use-modules (gnu))
> (use-service-modules networking ssh)
> (use-package-modules admin bootloaders)
> (operating-system
>   (host-name "ateguix")
>   (timezone "US/Eastern")
>   (locale "en_US.utf8")
>   (bootloader (grub-configuration (grub grub-efi) (device "/dev/sda")))
>   (file-systems (cons* (file-system
>                                               (device "/dev/sda4")
>                                               (mount-point "/")
>                         (type "ext4"))
>                                          (file-system
>                                               (device "/dev/sda2")
>                                               (mount-point "/boot/efi")
>                                               (type "vfat"))
>                                          %base-file-systems))
>   (users (cons (user-account
>                 (name "cinder")
>                 (comment "Main user")
>                 (group "users")
>                 (supplementary-groups '("wheel"
>                                         "audio" "video"))
>                 (home-directory "/home/cinder"))
>                %base-user-accounts))
>   (packages (cons tcpdump %base-packages))
>   (services (cons* (dhcp-client-service)
>                    (service openssh-service-type
>                             (openssh-configuration
>                               (port-number 2222)))
>                    %base-services)))

And for good measure, my filesystem info:

> Disk /dev/sda: 55.9 GiB, 60022480896 bytes, 117231408 sectors
> Units: sectors of 1 * 512 = 512 bytes
> Sector size (logical/physical): 512 bytes / 512 bytes
> I/O size (minimum/optimal): 512 bytes / 512 bytes
> Disklabel type: gpt
> Disk identifier: DAE2C6F8-2B05-408D-8EF3-7C4E49319651
> 
> Device         Start       End  Sectors  Size Type
> /dev/sda1       2048      6143     4096    2M BIOS boot
> /dev/sda2       6144   1054719  1048576  512M EFI System
> /dev/sda3    1054720  34609151 33554432   16G Linux swap
> /dev/sda4   34609152 101718015 67108864   32G Linux root (x86-64)
> /dev/sda5  101718016 117231374 15513359  7.4G Linux filesystem

Am I missing something simple in the config?

Thanks.