diff --git a/python/sglang/srt/managers/data_parallel_controller.py b/python/sglang/srt/managers/data_parallel_controller.py
index cbf14149e..6209852ad 100644
--- a/python/sglang/srt/managers/data_parallel_controller.py
+++ b/python/sglang/srt/managers/data_parallel_controller.py
@@ -447,6 +447,9 @@ class DataParallelController:
                 self.workers
             )
         else:
+            assert (
+                req.bootstrap_room is not None
+            ), "req.bootstrap_room should not be None. Do not send requests directly to prefill or decode instances, but send to the router instead."
             self.workers[req.bootstrap_room % len(self.workers)].send_pyobj(req)
 
     def shortest_queue_scheduler(self, req):