Package fails to configure on upgrade

$ sudo apt upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
1 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
Do you want to continue? [Y/n] y
Setting up grub-efi-amd64-signed (1.93.12+2.02-2ubuntu8.11) ...
/var/lib/dpkg/info/grub-efi-amd64-signed.postinst: 22: /var/lib/dpkg/info/grub-efi-amd64-signed.postinst: /usr/share/grub/grub-check-signatures: Permission denied
dpkg: error processing package grub-efi-amd64-signed (--configure):
 installed grub-efi-amd64-signed package post-installation script subprocess returned error exit status 126
Errors were encountered while processing:
 grub-efi-amd64-signed
E: Sub-process /usr/bin/dpkg returned an error code (1)

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: grub-efi-amd64-signed 1.93.12+2.02-2ubuntu8.11
ProcVersionSignature: Ubuntu 4.18.0-14.15~18.04.1-generic 4.18.20
Uname: Linux 4.18.0-14-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.5
Architecture: amd64
CurrentDesktop: Unity:Unity7:ubuntu
Date: Thu Feb 7 21:25:19 2019
InstallationDate: Installed on 2019-01-15 (23 days ago)
InstallationMedia: Ubuntu 18.04.1 LTS "Bionic Beaver" - Release amd64 (20180725)
SourcePackage: grub2-signed
UpgradeStatus: No upgrade log present (probably fresh install)