diff --git a/rag/llm/chat_model.py b/rag/llm/chat_model.py
index 4f37cf482..698264fbf 100644
--- a/rag/llm/chat_model.py
+++ b/rag/llm/chat_model.py
@@ -1075,6 +1075,9 @@ class GeminiChat(Base):
         for k in list(gen_conf.keys()):
             if k not in ["temperature", "top_p", "max_tokens"]:
                 del gen_conf[k]
+            # if max_tokens exists, rename it to max_output_tokens to match Gemini's API
+            if k == "max_tokens":
+                gen_conf["max_output_tokens"] = gen_conf.pop("max_tokens")
         return gen_conf
 
     def _chat(self, history, gen_conf={}, **kwargs):