diff --git a/configs/nixos/modules/shell/fish/default.nix b/configs/nixos/modules/shell/fish/default.nix
index 387c451..998f46d 100644
--- a/configs/nixos/modules/shell/fish/default.nix
+++ b/configs/nixos/modules/shell/fish/default.nix
@@ -30,6 +30,7 @@ in
     home-manager.users.${user} = {
       home.packages = with pkgs; [
         bat # backs the manpager
+        e2fsprogs # provides chattr and lsattr for the readonly function
         fastfetch # the shell greeting
       ];
 
@@ -99,6 +100,11 @@ in
             body = builtins.readFile ./functions/deploy-to.fish;
           };
 
+          readonly = {
+            description = "Toggle write protection for a Borderlands 2 save";
+            body = builtins.readFile ./functions/readonly.fish;
+          };
+
         };
 
         # Rendered by home-manager into ~/.config/fish/config.fish.
diff --git a/configs/nixos/modules/shell/fish/functions/readonly.fish b/configs/nixos/modules/shell/fish/functions/readonly.fish
new file mode 100644
index 0000000..0f10e9b
--- /dev/null
+++ b/configs/nixos/modules/shell/fish/functions/readonly.fish
@@ -0,0 +1,35 @@
+if test (count $argv) -ne 1
+    echo "usage: readonly <save-number>" >&2
+    return 2
+end
+
+set save_number $argv[1]
+if not string match --quiet --regex '^[0-9]{4}$' -- "$save_number"
+    echo "readonly: save number must contain four digits" >&2
+    return 2
+end
+
+set save_name "Save$save_number.sav"
+set save "$HOME/.local/share/Steam/steamapps/compatdata/49520/pfx/drive_c/users/steamuser/Documents/My games/Borderlands 2/WillowGame/SaveData/76561198060918970/$save_name"
+
+if not test -f "$save"
+    echo "readonly: save not found: $save" >&2
+    return 1
+end
+
+set attribute_output (lsattr -d -- "$save")
+or begin
+    echo "readonly: failed to read attributes for $save_name" >&2
+    return 1
+end
+
+set attribute_flags (string split --max 1 ' ' -- "$attribute_output")[1]
+if string match --quiet '*i*' -- "$attribute_flags"
+    sudo chattr -i -- "$save"
+    or return $status
+    echo "$save_name is now writable"
+else
+    sudo chattr +i -- "$save"
+    or return $status
+    echo "$save_name is now read-only"
+end