diff --git a/vllm/entrypoints/openai/serving_chat.py b/vllm/entrypoints/openai/serving_chat.py
index 934bd2a95063..d8cf6b0c0810 100644
--- a/vllm/entrypoints/openai/serving_chat.py
+++ b/vllm/entrypoints/openai/serving_chat.py
@@ -841,6 +841,8 @@ async def chat_completion_full_generator(
 
         request_metadata.final_usage_info = usage
 
+        self._clean_prompt_logprobs(final_res.prompt_logprobs)
+
         response = ChatCompletionResponse(
             id=request_id,
             created=created_time,
diff --git a/vllm/entrypoints/openai/serving_completion.py b/vllm/entrypoints/openai/serving_completion.py
index e7ad263e7fbe..bcbb83fdcd5a 100644
--- a/vllm/entrypoints/openai/serving_completion.py
+++ b/vllm/entrypoints/openai/serving_completion.py
@@ -396,13 +396,9 @@ def request_output_to_completion_response(
         for final_res in final_res_batch:
             prompt_token_ids = final_res.prompt_token_ids
             assert prompt_token_ids is not None
+            self._clean_prompt_logprobs(final_res.prompt_logprobs)
             prompt_logprobs = final_res.prompt_logprobs
-            if prompt_logprobs:
-                for logprob_dict in prompt_logprobs:
-                    if logprob_dict:
-                        for logprob_values in logprob_dict.values():
-                            if logprob_values.logprob == float('-inf'):
-                                logprob_values.logprob = -9999.0
+
             prompt_text = final_res.prompt
 
             token_ids: GenericSequence[int]
diff --git a/vllm/entrypoints/openai/serving_engine.py b/vllm/entrypoints/openai/serving_engine.py
index 785117ca1d45..da53c4134ffe 100644
--- a/vllm/entrypoints/openai/serving_engine.py
+++ b/vllm/entrypoints/openai/serving_engine.py
@@ -499,6 +499,20 @@ async def _get_trace_headers(
 
         return None
 
+    @staticmethod
+    def _clean_prompt_logprobs(
+            prompt_logprobs: Union[None, List[Union[None, Dict]]]) -> None:
+        """
+        Preprocess prompt_logprobs result 
+         to avoid starlette.response.JSONResponse's error
+        """
+        if prompt_logprobs:
+            for logprob_dict in prompt_logprobs:
+                if logprob_dict:
+                    for logprob_values in logprob_dict.values():
+                        if logprob_values.logprob == float('-inf'):
+                            logprob_values.logprob = -9999.0
+
     @staticmethod
     def _base_request_id(raw_request: Optional[Request],
                          default: Optional[str] = None) -> Optional[str]: