diff --git a/docling/backend/noop_backend.py b/docling/backend/noop_backend.py
index e4ae6d20..4974ba07 100644
--- a/docling/backend/noop_backend.py
+++ b/docling/backend/noop_backend.py
@@ -48,4 +48,4 @@ class NoOpBackend(AbstractDocumentBackend):
 
     @classmethod
     def supported_formats(cls) -> Set[InputFormat]:
-        return {InputFormat.AUDIO}
+        return set(InputFormat)