diff --git a/langfuse/langchain/CallbackHandler.py b/langfuse/langchain/CallbackHandler.py
index aba644a41..01b3b3829 100644
--- a/langfuse/langchain/CallbackHandler.py
+++ b/langfuse/langchain/CallbackHandler.py
@@ -594,7 +594,7 @@ def on_chain_start(
                     session_id=parsed_trace_attributes.get("session_id", None),
                     tags=parsed_trace_attributes.get("tags", None),
                     metadata=parsed_trace_attributes.get("metadata", None),
-                    trace_name=parsed_trace_attributes.get("trace_name", None),
+                    trace_name=parsed_trace_attributes.get("trace_name", span_name),
                 )
 
                 root_run_state = self._get_root_run_state(run_id)
diff --git a/tests/unit/test_langchain.py b/tests/unit/test_langchain.py
index 6f8fe458b..70e1f662c 100644
--- a/tests/unit/test_langchain.py
+++ b/tests/unit/test_langchain.py
@@ -1,6 +1,6 @@
 import importlib
 from contextvars import copy_context
-from unittest.mock import patch
+from unittest.mock import MagicMock, patch
 from uuid import uuid4
 
 import pytest
@@ -276,6 +276,27 @@ def test_root_chain_exports_when_end_runs_in_copied_context(
         otel_context.detach(context_token)
 
 
+def test_root_chain_propagates_run_name_as_default_trace_name():
+    handler = CallbackHandler()
+    run_id = uuid4()
+    propagation_context_manager = MagicMock()
+
+    with patch.object(
+        callback_handler_module,
+        "propagate_attributes",
+        return_value=propagation_context_manager,
+    ) as mock_propagate:
+        handler.on_chain_start(
+            {"id": ["langgraph", "Pregel"]},
+            {"messages": ["hello"]},
+            run_id=run_id,
+            name="my-agent",
+        )
+
+    mock_propagate.assert_called_once()
+    assert mock_propagate.call_args.kwargs["trace_name"] == "my-agent"
+
+
 def test_control_flow_errors_use_default_level_and_keep_status_message(
     langfuse_memory_client, get_span, monkeypatch
 ):