diff --git a/ernie_chat.py b/ernie_chat.py
index 2e6c99b..7a44f00 100644
--- a/ernie_chat.py
+++ b/ernie_chat.py
@@ -68,7 +68,7 @@ class ErnieChat(PyOperator):
                     elif k == 'answer':
                         new_m = {'role': 'assistant', 'content': v}
                     else:
-                        'Invalid message key: only accept key value from ["question", "answer"].'
+                        raise KeyError('Invalid message key: only accept key value from ["question", "answer"].')
                     new_messages.append(new_m)
         return new_messages