diff --git a/ray_elasticsearch/__init__.py b/ray_elasticsearch/__init__.py
index 1d85c0c..b6343c4 100644
--- a/ray_elasticsearch/__init__.py
+++ b/ray_elasticsearch/__init__.py
@@ -132,7 +132,11 @@ def iter_blocks() -> Iterator[Table]:
                     break
                 yield Table.from_pylist(
                     mapping=hits,
-                    schema=schema,
+                    schema=(
+                        schema
+                        if schema is not None and isinstance(schema, Schema)
+                        else None
+                    ),
                 )
                 search_after = max(
                     hit["sort"]