diff --git a/nixos/modules/system/boot/loader/grub/install-grub.pl b/nixos/modules/system/boot/loader/grub/install-grub.pl
index 6f0f62546a018a..bae85ac39491b0 100644
--- a/nixos/modules/system/boot/loader/grub/install-grub.pl
+++ b/nixos/modules/system/boot/loader/grub/install-grub.pl
@@ -113,56 +113,16 @@ sub runCommand {
     type => '$',
     mount => '$',
 });
-sub PathInMount {
-    my ($path, $mount) = @_;
-    my @splitMount = split /\//, $mount;
-    my @splitPath = split /\//, $path;
-    if ($#splitPath < $#splitMount) {
-        return 0;
-    }
-    for (my $i = 0; $i <= $#splitMount; $i++) {
-        if ($splitMount[$i] ne $splitPath[$i]) {
-            return 0;
-        }
-    }
-    return 1;
-}
 
 # Figure out what filesystem is used for the directory with init/initrd/kernel files
 sub GetFs {
     my ($dir) = @_;
-    my $bestFs = Fs->new(device => "", type => "", mount => "");
-    foreach my $fs (read_file("/proc/self/mountinfo")) {
-        chomp $fs;
-        my @fields = split / /, $fs;
-        my $mountPoint = $fields[4];
-        my @mountOptions = split /,/, $fields[5];
-
-        # Skip the optional fields.
-        my $n = 6; $n++ while $fields[$n] ne "-"; $n++;
-        my $fsType = $fields[$n];
-        my $device = $fields[$n + 1];
-        my @superOptions = split /,/, $fields[$n + 2];
-
-        # Skip the bind-mount on /nix/store.
-        next if $mountPoint eq "/nix/store" && (grep { $_ eq "rw" } @superOptions);
-        # Skip mount point generated by systemd-efi-boot-generator?
-        next if $fsType eq "autofs";
-
-        # Ensure this matches the intended directory
-        next unless PathInMount($dir, $mountPoint);
-
-        # Is it better than our current match?
-        if (length($mountPoint) > length($bestFs->mount)) {
-
-            # -d performs a stat, which can hang forever on network file systems,
-            # so we only make this call last, when it's likely that this is the mount point we need.
-            next unless -d $mountPoint;
-
-            $bestFs = Fs->new(device => $device, type => $fsType, mount => $mountPoint);
-        }
+    my ($status, @devInfo) = runCommand("@utillinux@/bin/findmnt", "-n", "-v", "-o", "SOURCE,FSTYPE,TARGET", "-T", @{[$dir]});
+    if ($status != 0 || $#devInfo != 1) {
+        die "Failed to get file system (returned $status) for @{[$dir]}";
     }
-    return $bestFs;
+    my @fields = split /\s+/, $devInfo[0];
+    return Fs->new(device => $fields[0], type => $fields[1], mount => $fields[2]);
 }
 struct (Grub => {
     path => '$',