diff --git a/gymnasium_robotics/envs/maze/ant_maze_v5.py b/gymnasium_robotics/envs/maze/ant_maze_v5.py
index 4b9d713d..f307f998 100644
--- a/gymnasium_robotics/envs/maze/ant_maze_v5.py
+++ b/gymnasium_robotics/envs/maze/ant_maze_v5.py
@@ -227,7 +227,7 @@ def __init__(
         reward_type: str = "sparse",
         continuing_task: bool = True,
         reset_target: bool = False,
-        xml_file: str | None = None,
+        xml_file: Union[str, None] = None,
         **kwargs,
     ):
         if xml_file is None: