diff --git a/py-denormalized/python/denormalized/datastream.py b/py-denormalized/python/denormalized/datastream.py
index 2af0d2f..c9b12f7 100644
--- a/py-denormalized/python/denormalized/datastream.py
+++ b/py-denormalized/python/denormalized/datastream.py
@@ -105,7 +105,7 @@ def window(
         group_expr: list[Expr],
         aggr_expr: list[Expr],
         window_length_millis: int,
-        slide_millis: int = None,
+        slide_millis: int | None = None,
     ) -> "DataStream":
         """Apply a windowing operation to the DataStream.