diff --git a/python/sglang/srt/managers/schedule_batch.py b/python/sglang/srt/managers/schedule_batch.py
index fdbc9b477cf6..0c178204a835 100644
--- a/python/sglang/srt/managers/schedule_batch.py
+++ b/python/sglang/srt/managers/schedule_batch.py
@@ -2266,6 +2266,7 @@ def merge_batch(self, other: "ScheduleBatch"):
         self.has_stream |= other.has_stream
         self.has_grammar |= other.has_grammar
         self.return_hidden_states |= other.return_hidden_states
+        self.is_prefill_only = self.is_prefill_only and other.is_prefill_only
 
         if self.spec_info:
             self.spec_info.merge_batch(other.spec_info)