diff --git a/aperisolve/app.py b/aperisolve/app.py
index 235de2e..5e92077 100644
--- a/aperisolve/app.py
+++ b/aperisolve/app.py
@@ -39,7 +39,8 @@ def too_large(_: Any) -> tuple[Response, int]:
 
 
 @app.errorhandler(404)
-def not_found(e):
+def not_found(_: Any) -> str:
+    """Error Handler for 404 not found."""
     return render_template("error.html", message="Ressource not found", statuscode=404)