using files from the syslinux package and 2 from kernel.org/.../syslinux-6.04-pre1.tar
target=/media/sdc sudo apt install syslinux wget -N https://mirrors.edge.kernel.org/pub/linux/utils/boot/syslinux/Testing/6.04/syslinux-6.04-pre1.tar.gz tar xf syslinux-6.04-pre1.tar.gz mkdir -p $target/EFI/syslinux $target/EFI/BOOT cp syslinux-6.04-pre1/efi64/efi/syslinux.efi $target/EFI/BOOT/BOOTX64.EFI cp syslinux-6.04-pre1/efi64/com32/elflink/ldlinux/ldlinux.e64 $target/EFI/BOOT/ cp /usr/lib/syslinux/modules/efi64/* $target/EFI/syslinux I think the fix will be something like the above (sans wget) and the cp lines be added around here: https://salsa.debian.org/installer-team/debian-installer/blob/master/build/config/x86.cfg#L113-115 mcopy -i$(TEMP_BOOT) /usr/lib/syslinux/modules/bios/vesamenu.c32 ::vesamenu.c32; \ mcopy -i$(TEMP_BOOT) /usr/lib/syslinux/modules/bios/libcom32.c32 ::libcom32.c32; \ mcopy -i$(TEMP_BOOT) /usr/lib/syslinux/modules/bios/libutil.c32 ::libutil.c32 ; \ -- Carl K