diff --git a/black.py b/black.py
index 2664672a6d6..1084b9ca9f4 100644
--- a/black.py
+++ b/black.py
@@ -2788,7 +2788,9 @@ def get_future_imports(node: Node) -> Set[str]:
     return imports
 
 
-def gen_python_files_in_dir(path: Path, include, exclude) -> Iterator[Path]:
+def gen_python_files_in_dir(
+    path: Path, include: Pattern[str], exclude: Pattern[str]
+) -> Iterator[Path]:
     """Generate all files under `path` whose paths are not excluded by the
     `exclude` regex, but are included by the `include` regex.
     """