diff --git a/vllm/entrypoints/openai/serving_responses.py b/vllm/entrypoints/openai/serving_responses.py
index 899cb07b2b37..d02afb4531e0 100644
--- a/vllm/entrypoints/openai/serving_responses.py
+++ b/vllm/entrypoints/openai/serving_responses.py
@@ -734,6 +734,11 @@ def _construct_input_messages_with_harmony(
                 # parsing the tool call output.
                 if isinstance(response_msg, ResponseFunctionToolCall):
                     prev_outputs.append(response_msg)
+                elif isinstance(
+                        response_msg,
+                        dict) and response_msg.get("type") == "function_call":
+                    prev_outputs.append(
+                        ResponseFunctionToolCall(**response_msg))
         return messages
 
     async def _run_background_request(