diff --git a/vllm/v1/engine/output_processor.py b/vllm/v1/engine/output_processor.py
index 3be6c4821214..8bb25268c9cd 100644
--- a/vllm/v1/engine/output_processor.py
+++ b/vllm/v1/engine/output_processor.py
@@ -34,6 +34,7 @@ def __init__(self, output_kind: RequestOutputKind):
         self.aggregate = output_kind == RequestOutputKind.DELTA
         self.output: Optional[Union[RequestOutput, PoolingRequestOutput,
                                     Exception]] = None
+        self._loop = asyncio.get_running_loop()
         self.ready = asyncio.Event()
 
     def put(self, output: Union[RequestOutput, PoolingRequestOutput,
@@ -41,7 +42,7 @@ def put(self, output: Union[RequestOutput, PoolingRequestOutput,
         """Non-blocking put operation."""
         if self.output is None or isinstance(output, Exception):
             self.output = output
-            self.ready.set()
+            self._loop.call_soon_threadsafe(self.ready.set)
         elif isinstance(self.output, (RequestOutput, PoolingRequestOutput)):
             # This ensures that request outputs with different request indexes
             # (if n > 1) do not override each other.
@@ -353,17 +354,17 @@ def process_outputs(
         1) Compute stats for logging
         2) Detokenize
         3) Create and handle RequestOutput objects:
-            * If there is a queue (for usage with AsyncLLM), 
+            * If there is a queue (for usage with AsyncLLM),
               put the RequestOutput objects into the queue for
               handling by the per-request generate() tasks.
 
-            * If there is no queue (for usage with LLMEngine), 
+            * If there is no queue (for usage with LLMEngine),
               return a list of RequestOutput objects.
 
         NOTE FOR DEVELOPERS
 
         vLLM V1 minimizes the number of python loops over the full
-        batch to ensure system overheads are minimized. This is the 
+        batch to ensure system overheads are minimized. This is the
         only function that should loop over EngineCoreOutputs.
 
         If you need to touch every element of the batch, do it from