diff --git a/api/db/services/dialog_service.py b/api/db/services/dialog_service.py
index d2efd559e..c98756ae1 100644
--- a/api/db/services/dialog_service.py
+++ b/api/db/services/dialog_service.py
@@ -109,6 +109,7 @@ def chat_solo(dialog, messages, stream=True):
     msg = [{"role": m["role"], "content": re.sub(r"##\d+\$\$", "", m["content"])} for m in messages if m["role"] != "system"]
     if stream:
         last_ans = ""
+        delta_ans = ""
         for ans in chat_mdl.chat_streamly(prompt_config.get("system", ""), msg, dialog.llm_setting):
             answer = ans
             delta_ans = ans[len(last_ans) :]
@@ -116,6 +117,7 @@ def chat_solo(dialog, messages, stream=True):
                 continue
             last_ans = answer
             yield {"answer": answer, "reference": {}, "audio_binary": tts(tts_mdl, delta_ans), "prompt": "", "created_at": time.time()}
+            delta_ans = ""
         if delta_ans:
             yield {"answer": answer, "reference": {}, "audio_binary": tts(tts_mdl, delta_ans), "prompt": "", "created_at": time.time()}
     else: