diff --git a/black.py b/black.py
index 320abd3ab72..9485e6931ca 100644
--- a/black.py
+++ b/black.py
@@ -3409,7 +3409,7 @@ def get_imports_from_children(children: List[LN]) -> Generator[str, None, None]:
 
 
 def gen_python_files(
-    paths: [Path],
+    paths: Iterable[Path],
     root: Path,
     include: Optional[Pattern[str]],
     exclude: Pattern[str],
@@ -3454,11 +3454,11 @@ def gen_python_files(
 def gen_python_files_in_dir(
     path: Path,
     root: Path,
-    include: Pattern[str],
+    include: Optional[Pattern[str]],
     exclude: Pattern[str],
     report: "Report",
 ) -> Iterator[Path]:
-    return gen_python_files(path.iterdir())
+    return gen_python_files(path.iterdir(), root, include, exclude, report)