diff --git a/rsconcept/backend/apps/oss/views/oss.py b/rsconcept/backend/apps/oss/views/oss.py
index 3d1943b8..0911bf90 100644
--- a/rsconcept/backend/apps/oss/views/oss.py
+++ b/rsconcept/backend/apps/oss/views/oss.py
@@ -357,7 +357,7 @@ class OssViewSet(viewsets.GenericViewSet, generics.ListAPIView, generics.Retriev
             source = cast(m.Operation, serializer.validated_data['source_operation'])
             alias = '+' + source.alias
             title = '+' + source.title
-            source_schema = RSForm(source.result)
+            source_schema = RSForm(cast(LibraryItem, source.result))
 
             new_schema = deepcopy(source_schema.model)
             new_schema.pk = None