diff --git a/litellm/responses/litellm_completion_transformation/streaming_iterator.py b/litellm/responses/litellm_completion_transformation/streaming_iterator.py
index 6b13c9d4297..beffd12a349 100644
--- a/litellm/responses/litellm_completion_transformation/streaming_iterator.py
+++ b/litellm/responses/litellm_completion_transformation/streaming_iterator.py
@@ -599,7 +599,9 @@ class LiteLLMCompletionStreamingIterator(ResponsesAPIStreamingIterator):
             self._cached_item_id = f"msg_{uuid.uuid4()}"
         self.sent_message_item_added_event = True
         self.sent_content_part_added_event = True
-        self._message_output_index = 1 if self._cached_reasoning_item_id is not None else 0
+        if self._cached_reasoning_item_id is not None:
+            self._message_output_index = self._next_tool_output_index
+            self._next_tool_output_index += 1
         self._sequence_number += 1
         event: Final = OutputItemAddedEvent(
             type=ResponsesAPIStreamEvents.OUTPUT_ITEM_ADDED,
@@ -953,7 +955,6 @@ class LiteLLMCompletionStreamingIterator(ResponsesAPIStreamingIterator):
             if self._cached_reasoning_item_id is None:
                 self._cached_reasoning_item_id = f"rs_{uuid.uuid4()}"
             self._reasoning_item_id = self._cached_reasoning_item_id
-            self._next_tool_output_index = max(self._next_tool_output_index, 2)
 
             event = OutputItemAddedEvent(
                 type=ResponsesAPIStreamEvents.OUTPUT_ITEM_ADDED,
diff --git a/tests/test_litellm/responses/litellm_completion_transformation/test_streaming_iterator_transformation.py b/tests/test_litellm/responses/litellm_completion_transformation/test_streaming_iterator_transformation.py
index 895f59632c7..c727a5be4bc 100644
--- a/tests/test_litellm/responses/litellm_completion_transformation/test_streaming_iterator_transformation.py
+++ b/tests/test_litellm/responses/litellm_completion_transformation/test_streaming_iterator_transformation.py
@@ -1063,6 +1063,34 @@ async def test_reasoning_then_text_announces_message_item_before_text_events(syn
     assert announced_indexes_by_item_type["message"] != announced_indexes_by_item_type["reasoning"]
 
 
+@pytest.mark.parametrize("sync_mode", [True, False])
+@pytest.mark.asyncio
+async def test_tool_then_reasoning_then_text_gives_message_its_own_output_index(sync_mode):
+    iterator: Final = _build_iterator(
+        [
+            _tool_call_chunk(),
+            _reasoning_chunk("thinking"),
+            _chunk("Hello"),
+            _chunk("!", finish_reason="stop"),
+        ]
+    )
+
+    events: Final = await _collect_events(iterator, sync_mode)
+    output_item_added_events: Final = [
+        event for event in events if getattr(event, "type", None) == ResponsesAPIStreamEvents.OUTPUT_ITEM_ADDED
+    ]
+    message_item_adds: Final = [event for event in output_item_added_events if _is_message_item(event)]
+    function_call_adds: Final = [
+        event for event in output_item_added_events if getattr(event.item, "type", None) == "function_call"
+    ]
+
+    assert len(message_item_adds) == 1
+    assert all(message_item_adds[0].output_index != event.output_index for event in function_call_adds)
+
+    output_indexes_by_item_id: Final = {event.item.id: event.output_index for event in output_item_added_events}
+    assert len(output_indexes_by_item_id) == len(set(output_indexes_by_item_id.values()))
+
+
 @pytest.mark.parametrize("sync_mode", [True, False])
 @pytest.mark.asyncio
 async def test_plain_text_stream_announces_exactly_one_message_item(sync_mode):