installer could not install grub

[jwwinship]

I wanted to install ubuntu 16.04. I used a GPT partition and installed a boot partition (EXT4). It failed saying that it could not install grub on / partition..

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubiquity 2.21.51 [modified: lib/partman/automatically_partition/question]
ProcVersionSignature: Ubuntu 4.4.0-15.31-generic 4.4.6
Uname: Linux 4.4.0-15-generic x86_64
ApportVersion: 2.20-0ubuntu3
Architecture: amd64
CasperVersion: 1.368
Date: Fri May 13 19:18:44 2016
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz.efi file=/cdrom/preseed/ubuntu.seed boot=casper quiet splash ---
LiveMediaBuild: Ubuntu 16.04 LTS "Xenial Xerus" - Beta amd64 (20160323)
ProcEnviron:
 LANGUAGE=en_AU.UTF-8
 PATH=(custom, no user)
 LANG=en_AU.UTF-8
 SHELL=/bin/bash
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)

[Phillip Susi (psusi)]

You are trying to install in UEFI mode. To do this, you must create an EFI system partition on the disk.