diff --git a/engine/core/duplex_pipeline.py b/engine/core/duplex_pipeline.py
index a4fe91b..6e7a0ea 100644
--- a/engine/core/duplex_pipeline.py
+++ b/engine/core/duplex_pipeline.py
@@ -813,6 +813,12 @@ class DuplexPipeline:
         # Prime ASR with a short pre-speech context window so the utterance
         # start isn't lost while waiting for VAD to transition to Speech.
         pre_roll = self._pre_speech_buffer
+        # _pre_speech_buffer already includes current speech frames; avoid
+        # duplicating onset audio when we append pending speech below.
+        if self._pending_speech_audio and len(pre_roll) > len(self._pending_speech_audio):
+            pre_roll = pre_roll[:-len(self._pending_speech_audio)]
+        elif self._pending_speech_audio:
+            pre_roll = b""
         capture_audio = pre_roll + self._pending_speech_audio
         if capture_audio:
             await self.asr_service.send_audio(capture_audio)