diff --git a/data_safe_haven/cli.py b/data_safe_haven/cli.py
index ef6a67aa75..111ee9d13b 100644
--- a/data_safe_haven/cli.py
+++ b/data_safe_haven/cli.py
@@ -31,7 +31,7 @@ def callback(
         ),
     ] = None,
     version: Annotated[
-        bool | None,
+        Optional[bool],
         typer.Option("--version", "-V", help="Display the version of this application."),
     ] = None,
 ) -> None: