diff --git a/astrbot/core/provider/sources/openai_source.py b/astrbot/core/provider/sources/openai_source.py
index d64feb5a07..68fad067b0 100644
--- a/astrbot/core/provider/sources/openai_source.py
+++ b/astrbot/core/provider/sources/openai_source.py
@@ -334,11 +334,15 @@ async def _query_stream(
             choice = chunk.choices[0]
             delta = choice.delta
 
-            # siliconflow workaround
             if dtcs := delta.tool_calls:
-                for tc in dtcs:
+                for idx, tc in enumerate(dtcs):
+                    # siliconflow workaround
                     if tc.function and tc.function.arguments:
                         tc.type = "function"
+                    # Fix for #6661: Add missing 'index' field to tool_call deltas
+                    # Gemini and some OpenAI-compatible proxies omit this field
+                    if not hasattr(tc, "index") or tc.index is None:
+                        tc.index = idx
             try:
                 state.handle_chunk(chunk)
             except Exception as e: