diff --git a/PFERD/errors.py b/PFERD/errors.py
index 014479d..d003314 100644
--- a/PFERD/errors.py
+++ b/PFERD/errors.py
@@ -3,7 +3,7 @@ An error logging decorator.
 """
 
 import logging
-from typing import Any, Callable
+from typing import Any, Callable, TypeVar, cast
 
 from rich.console import Console
 
@@ -19,7 +19,10 @@ class FatalException(Exception):
     """
 
 
-def swallow_and_print_errors(function: Callable) -> Callable:
+TFun = TypeVar('TFun', bound=Callable[..., Any])
+
+
+def swallow_and_print_errors(function: TFun) -> TFun:
     """
     Decorates a function, swallows all errors, logs them and returns none if one occurred.
     """
@@ -33,4 +36,4 @@ def swallow_and_print_errors(function: Callable) -> Callable:
         except Exception as error:
             Console().print_exception()
             return None
-    return inner
+    return cast(TFun, inner)
diff --git a/example_config.py b/example_config.py
index 5da95de..6b1c5d3 100644
--- a/example_config.py
+++ b/example_config.py
@@ -2,6 +2,7 @@ import argparse
 from pathlib import Path, PurePath
 
 from PFERD import Pferd
+from PFERD.ilias import IliasDirectoryType
 from PFERD.transform import (attempt, do, glob, keep, move, move_dir,
                              optionally, re_move, re_rename)
 
@@ -48,7 +49,7 @@ tf_ss_2020_pg = attempt(
 )
 
 
-def df_ss_2020_or1(path: PurePath) -> bool:
+def df_ss_2020_or1(path: PurePath, _type: IliasDirectoryType) -> bool:
     if glob("Tutorien/")(path):
         return True
     if glob("Tutorien/Tutorium 10, dienstags 15:45 Uhr/")(path):