diff --git a/dangerzone/document.py b/dangerzone/document.py
index 5fc1eda..8af46f0 100644
--- a/dangerzone/document.py
+++ b/dangerzone/document.py
@@ -124,7 +124,7 @@ class Document:
         self._output_filename = filename
 
     @property
-    def sanitized_output_filename(self) -> None:
+    def sanitized_output_filename(self) -> str:
         return util.replace_control_chars(self.output_filename)
 
     @property