diff --git a/nixos/modules/system/boot/loader/grub/install-grub.pl b/nixos/modules/system/boot/loader/grub/install-grub.pl
index 668e74a9722e..2dad8b36db32 100644
--- a/nixos/modules/system/boot/loader/grub/install-grub.pl
+++ b/nixos/modules/system/boot/loader/grub/install-grub.pl
@@ -122,7 +122,7 @@ sub GrubFs {
                 # Based on the type pull in the identifier from the system
                 my ($status, @devInfo) = runCommand("blkid -o export @{[$fs->device]}");
                 if ($status != 0) {
-                    die "Failed to get blkid info for @{[$fs->device]}";
+                    die "Failed to get blkid info for @{[$fs->mount]} on @{[$fs->device]}";
                 }
                 my @matches = join("", @devInfo) =~ m/@{[uc $fsIdentifier]}=([^\n]*)/;
                 if ($#matches != 0) {
@@ -164,8 +164,7 @@ sub GrubFs {
     return Grub->new(path => $path, search => $search);
 }
 my $grubBoot = GrubFs("/boot");
-# FIXME: Should be /nix/store, but this fails in the installer
-my $grubStore = GrubFs("/nix");
+my $grubStore = GrubFs("/nix/store");
 
 # Generate the header.
 my $conf .= "# Automatically generated.  DO NOT EDIT THIS FILE!\n";
@@ -244,7 +243,7 @@ mkpath("/boot/kernels", 0, 0755) if $copyKernels;
 
 sub copyToKernelsDir {
     my ($path) = @_;
-    return $grubStore->path . substr($path, length("/nix")) unless $copyKernels;
+    return $grubStore->path . substr($path, length("/nix/store")) unless $copyKernels;
     $path =~ /\/nix\/store\/(.*)/ or die;
     my $name = $1; $name =~ s/\//-/g;
     my $dst = "/boot/kernels/$name";