Package: debian-installer Version: 20160630 When using a GPT partition table with a BIOS-based system (not EFI), a small Bios Boot Partition is required by Grub for embedding, see https://en.wikipedia.org/wiki/BIOS_boot_partition
However, partman does not display a warning when this partition is missing. Instead, installation proceeds normally, but at the very end of the installation, grub fails to install because of the missing partition. This is using debian-installer Stretch Alpha 7. Note: I am not sure the debian-installer actually allows to create a GPT partition table. This situation happened using a disk with a pre-existing GPT partition table. Regards,