diff --git a/lightrag/operate.py b/lightrag/operate.py
index a0111719..987fc7bb 100644
--- a/lightrag/operate.py
+++ b/lightrag/operate.py
@@ -301,7 +301,7 @@ async def _merge_edges_then_upsert(
                 node_data={
                     "source_id": source_id,
                     "description": description,
-                    "entity_type": '"UNKNOWN"',
+                    "entity_type": "UNKNOWN",
                 },
             )
     description = await _handle_entity_relation_summary(