diff --git a/configs/init-functions.el b/configs/init-functions.el
index 94b9768..d29f07d 100644
--- a/configs/init-functions.el
+++ b/configs/init-functions.el
@@ -159,5 +159,15 @@ If PROJECT is not specified, assume current project root."
   (global-corfu-mode 1)
   )
 
+(defun force-fundamental-for-large-files ()
+  "If a file is over 5MB, open it in fundamental-mode and disable undo."
+  (when (> (buffer-size) (* 5 1024 1024))
+    (setq buffer-read-only t)
+    (buffer-disable-undo)
+    (fundamental-mode)
+    (message "Buffer set to fundamental-mode and read-only due to size.")))
+
+(add-hook 'find-file-hook #'force-fundamental-for-large-files)
+
 (provide 'init-functions)
 ;;; init-functions.el ends here.