diff --git a/src/services/kiaai/chat.py b/src/services/kiaai/chat.py
index 8442803..b83e067 100644
--- a/src/services/kiaai/chat.py
+++ b/src/services/kiaai/chat.py
@@ -1,4 +1,5 @@
 import json
+import codecs
 import asyncio
 from typing import AsyncGenerator
 import httpx
@@ -145,9 +146,12 @@ class KiaAIService:
                 line_count = 0
                 buf = ""
                 done = False
+                # Incremental decoder holds partial multi-byte chars (Persian = 2 bytes each)
+                # until the remaining bytes arrive — prevents '?' corruption with chunk_size=1
+                _decoder = codecs.getincrementaldecoder("utf-8")(errors="replace")
 
                 async for raw in resp.aiter_bytes(chunk_size=1):
-                    buf += raw.decode("utf-8", errors="replace")
+                    buf += _decoder.decode(raw)
 
                     while "\n" in buf:
                         line, buf = buf.split("\n", 1)