diff --git a/metagpt/provider/base_gpt_api.py b/metagpt/provider/base_gpt_api.py
index 19f5fcfff..59da67d5b 100644
--- a/metagpt/provider/base_gpt_api.py
+++ b/metagpt/provider/base_gpt_api.py
@@ -48,6 +48,8 @@ class BaseGPTAPI(BaseChatbot):
         message = []
         if system_msgs:
             message = self._system_msgs(system_msgs)
+        else:
+            message = [self._default_system_msg()]
         if format_msgs:
             message.extend(format_msgs)
         message.append(self._user_msg(msg))