diff --git a/vllm/entrypoints/openai/protocol.py b/vllm/entrypoints/openai/protocol.py
index 8b60b7a70b121..3b35ae1ebd705 100644
--- a/vllm/entrypoints/openai/protocol.py
+++ b/vllm/entrypoints/openai/protocol.py
@@ -216,9 +216,13 @@ class ChatCompletionRequest(OpenAIBaseModel):
     # doc: end-chat-completion-extra-params
 
     def to_sampling_params(
-        self, tokenizer: PreTrainedTokenizer,
-        guided_decode_logits_processor: Optional[LogitsProcessor]
-    ) -> SamplingParams:
+            self, tokenizer: PreTrainedTokenizer,
+            guided_decode_logits_processor: Optional[LogitsProcessor],
+            default_max_tokens: int) -> SamplingParams:
+        max_tokens = self.max_tokens
+        if max_tokens is None:
+            max_tokens = default_max_tokens
+
         # We now allow logprobs being true without top_logrobs.
         logits_processors = get_logits_processors(
             logit_bias=self.logit_bias,
@@ -244,7 +248,7 @@ def to_sampling_params(
             logprobs=self.top_logprobs if self.logprobs else None,
             prompt_logprobs=self.top_logprobs if self.echo else None,
             ignore_eos=self.ignore_eos,
-            max_tokens=self.max_tokens,
+            max_tokens=max_tokens,
             min_tokens=self.min_tokens,
             use_beam_search=self.use_beam_search,
             early_stopping=self.early_stopping,
@@ -399,9 +403,13 @@ class CompletionRequest(OpenAIBaseModel):
     # doc: end-completion-extra-params
 
     def to_sampling_params(
-        self, tokenizer: PreTrainedTokenizer,
-        guided_decode_logits_processor: Optional[LogitsProcessor]
-    ) -> SamplingParams:
+            self, tokenizer: PreTrainedTokenizer,
+            guided_decode_logits_processor: Optional[LogitsProcessor],
+            default_max_tokens: int) -> SamplingParams:
+        max_tokens = self.max_tokens
+        if max_tokens is None:
+            max_tokens = default_max_tokens
+
         echo_without_generation = self.echo and self.max_tokens == 0
 
         logits_processors = get_logits_processors(
@@ -427,7 +435,7 @@ def to_sampling_params(
             stop_token_ids=self.stop_token_ids,
             logprobs=self.logprobs,
             ignore_eos=self.ignore_eos,
-            max_tokens=self.max_tokens if not echo_without_generation else 1,
+            max_tokens=max_tokens if not echo_without_generation else 1,
             min_tokens=self.min_tokens,
             use_beam_search=self.use_beam_search,
             early_stopping=self.early_stopping,
diff --git a/vllm/entrypoints/openai/serving_chat.py b/vllm/entrypoints/openai/serving_chat.py
index 1dee798858a16..c832cf2a24b50 100644
--- a/vllm/entrypoints/openai/serving_chat.py
+++ b/vllm/entrypoints/openai/serving_chat.py
@@ -144,10 +144,10 @@ async def create_chat_completion(
             )
 
             sampling_params = request.to_sampling_params(
-                tokenizer, guided_decode_logits_processor)
-            if sampling_params.max_tokens is None:
-                sampling_params.max_tokens = \
-                    self.max_model_len - len(prompt_inputs["prompt_token_ids"])
+                tokenizer,
+                guided_decode_logits_processor,
+                default_max_tokens=self.max_model_len -
+                len(prompt_inputs["prompt_token_ids"]))
 
             self._log_inputs(request_id,
                              prompt_inputs,
diff --git a/vllm/entrypoints/openai/serving_completion.py b/vllm/entrypoints/openai/serving_completion.py
index 51de2f1826554..7765c5903f341 100644
--- a/vllm/entrypoints/openai/serving_completion.py
+++ b/vllm/entrypoints/openai/serving_completion.py
@@ -106,10 +106,10 @@ async def create_completion(self, request: CompletionRequest,
 
             for i, prompt_inputs in enumerate(prompts):
                 sampling_params = request.to_sampling_params(
-                    tokenizer, guided_decode_logits_processor)
-                if sampling_params.max_tokens is None:
-                    sampling_params.max_tokens = self.max_model_len - \
-                        len(prompt_inputs["prompt_token_ids"])
+                    tokenizer,
+                    guided_decode_logits_processor,
+                    default_max_tokens=self.max_model_len -
+                    len(prompt_inputs["prompt_token_ids"]))
 
                 request_id_item = f"{request_id}-{i}"