diff --git a/tests/mq_llm_engine/test_error_handling.py b/tests/mq_llm_engine/test_error_handling.py
index 49b02279d..3feee01da 100644
--- a/tests/mq_llm_engine/test_error_handling.py
+++ b/tests/mq_llm_engine/test_error_handling.py
@@ -66,7 +66,7 @@ async def test_evil_forward(tmp_socket):
         with pytest.raises(MQEngineDeadError):
             async for _ in client.generate(prompt="Hello my name is",
                                            sampling_params=SamplingParams(),
-                                           request_id=uuid.uuid4()):
+                                           request_id=str(uuid.uuid4())):
                 pass
         assert client.errored
 
@@ -115,7 +115,7 @@ async def test_failed_health_check(tmp_socket):
         with pytest.raises(MQEngineDeadError):
             async for _ in client.generate(prompt="Hello my name is",
                                            sampling_params=SamplingParams(),
-                                           request_id=uuid.uuid4()):
+                                           request_id=str(uuid.uuid4())):
                 pass
 
         client.close()
@@ -157,7 +157,7 @@ async def test_failed_abort(tmp_socket):
             async for _ in client.generate(
                     prompt="Hello my name is",
                     sampling_params=SamplingParams(max_tokens=10),
-                    request_id=uuid.uuid4()):
+                    request_id=str(uuid.uuid4())):
                 pass
         assert "KeyError" in repr(execinfo.value)
         assert client.errored
@@ -189,7 +189,7 @@ async def test_batch_error(tmp_socket):
             params = SamplingParams(min_tokens=2048, max_tokens=2048)
             async for _ in client.generate(prompt="Hello my name is",
                                            sampling_params=params,
-                                           request_id=uuid.uuid4()):
+                                           request_id=str(uuid.uuid4())):
                 pass
 
         tasks = [asyncio.create_task(do_generate(client)) for _ in range(10)]
@@ -289,7 +289,7 @@ async def test_engine_process_death(tmp_socket):
         with pytest.raises(MQEngineDeadError):
             async for _ in client.generate(prompt="Hello my name is",
                                            sampling_params=SamplingParams(),
-                                           request_id=uuid.uuid4()):
+                                           request_id=str(uuid.uuid4())):
                 pass
 
         # And the health check should show the engine is dead
diff --git a/vllm/engine/llm_engine.py b/vllm/engine/llm_engine.py
index 8fccf9bd2..25fa1c305 100644
--- a/vllm/engine/llm_engine.py
+++ b/vllm/engine/llm_engine.py
@@ -687,6 +687,10 @@ class LLMEngine:
             >>> # continue the request processing
             >>> ...
         """
+        if not isinstance(request_id, str):
+            raise TypeError(
+                f"request_id must be a string, got {type(request_id)}")
+
         if lora_request is not None and not self.lora_config:
             raise ValueError(f"Got lora_request {lora_request} but LoRA is "
                              "not enabled!")
diff --git a/vllm/v1/engine/llm_engine.py b/vllm/v1/engine/llm_engine.py
index 25fab2713..a2328c37b 100644
--- a/vllm/v1/engine/llm_engine.py
+++ b/vllm/v1/engine/llm_engine.py
@@ -192,6 +192,11 @@ class LLMEngine:
         prompt_adapter_request: Optional[PromptAdapterRequest] = None,
         priority: int = 0,
     ) -> None:
+        # Validate the request_id type.
+        if not isinstance(request_id, str):
+            raise TypeError(
+                f"request_id must be a string, got {type(request_id)}")
+
         # Process raw inputs into the request.
         prompt_str, request = self.processor.process_inputs(
             request_id, prompt, params, arrival_time, lora_request,