diff --git a/python/sglang/srt/managers/scheduler.py b/python/sglang/srt/managers/scheduler.py
index 31294749d..b84608e06 100644
--- a/python/sglang/srt/managers/scheduler.py
+++ b/python/sglang/srt/managers/scheduler.py
@@ -2297,8 +2297,9 @@ class Scheduler(
     def set_next_batch_sampling_info_done(self, batch: ScheduleBatch):
         if batch.next_batch_sampling_info:
             if batch.next_batch_sampling_info.grammars is not None:
-                batch.next_batch_sampling_info.update_regex_vocab_mask()
-                self.current_stream.synchronize()
+                if self.disaggregation_mode != DisaggregationMode.PREFILL:
+                    batch.next_batch_sampling_info.update_regex_vocab_mask()
+                    self.current_stream.synchronize()
             batch.next_batch_sampling_info.sampling_info_done.set()
 
     def watchdog_thread(self):