diff --git a/src/mplcyberpunk/core.py b/src/mplcyberpunk/core.py
index e01467b..6e6f4f9 100644
--- a/src/mplcyberpunk/core.py
+++ b/src/mplcyberpunk/core.py
@@ -27,7 +27,7 @@ def make_lines_glow(
     n_glow_lines: int = 10,
     diff_linewidth: float = 1.05,
     alpha_line: float = 0.3,
-    lines: Union[Line2D, List[Line2D]] = None,
+    lines: Optional[Union[Line2D, List[Line2D]]] = None,
 ) -> None:
     """Add a glow effect to the lines in an axis object.