diff --git a/metagpt/provider/base_llm.py b/metagpt/provider/base_llm.py
index 52dd96b1a..d23d162c8 100644
--- a/metagpt/provider/base_llm.py
+++ b/metagpt/provider/base_llm.py
@@ -43,7 +43,9 @@ class BaseLLM(ABC):
         if system_msgs:
             message = self._system_msgs(system_msgs)
         else:
-            message = [self._default_system_msg()] if self.use_system_prompt else []
+            message = [self._default_system_msg()]
+        if not self.use_system_prompt:
+            message = []
         if format_msgs:
             message.extend(format_msgs)
         message.append(self._user_msg(msg))
diff --git a/tests/mock/mock_llm.py b/tests/mock/mock_llm.py
index 6e7a1cdd5..35e0e9ee9 100644
--- a/tests/mock/mock_llm.py
+++ b/tests/mock/mock_llm.py
@@ -41,7 +41,9 @@ class MockLLM(OpenAILLM):
         if system_msgs:
             message = self._system_msgs(system_msgs)
         else:
-            message = [self._default_system_msg()] if self.use_system_prompt else []
+            message = [self._default_system_msg()]
+        if not self.use_system_prompt:
+            message = []
         if format_msgs:
             message.extend(format_msgs)
         message.append(self._user_msg(msg))