diff --git a/dangerzone/isolation_provider/qubes.py b/dangerzone/isolation_provider/qubes.py
index 54d23e9..e620123 100644
--- a/dangerzone/isolation_provider/qubes.py
+++ b/dangerzone/isolation_provider/qubes.py
@@ -67,7 +67,7 @@ class Qubes(IsolationProvider):
     def _convert(
         self,
         document: Document,
-        ocr_lang: Optional[str],
+        ocr_lang: Optional[str] = None,
     ) -> bool:
         success = False