diff --git a/dangerzone/gui/__init__.py b/dangerzone/gui/__init__.py
index 89241bd..a0e6f96 100644
--- a/dangerzone/gui/__init__.py
+++ b/dangerzone/gui/__init__.py
@@ -47,7 +47,7 @@ class ApplicationWrapper(QtCore.QObject):
 
 @click.command()
 @click.argument("filename", required=False)
-def gui_main(filename: str) -> bool:
+def gui_main(filename: Optional[str]) -> bool:
     setup_logging()
 
     if platform.system() == "Darwin":