diff --git a/fastchat/serve/model_worker.py b/fastchat/serve/model_worker.py
index 683a78556..6e29f9916 100644
--- a/fastchat/serve/model_worker.py
+++ b/fastchat/serve/model_worker.py
@@ -333,7 +333,7 @@ def create_model_worker():
         help="Overwrite the random seed for each generation.",
     )
     parser.add_argument(
-        "--debug", type=bool, default=False, help="Print debugging messages"
+        "--debug", action="store_true", help="Print debugging messages"
     )
     parser.add_argument(
         "--ssl",