fix typo
diff --git a/fastchat/train/train_lora.py b/fastchat/train/train_lora.py
index 24c8b8978b..b2fa0a844c 100644
--- a/fastchat/train/train_lora.py
+++ b/fastchat/train/train_lora.py
@@ -41,7 +41,7 @@
 
 @dataclass
 class TrainingArguments(transformers.TrainingArguments):
-    cache_dir: Optional[str] = field(default=None)
+    cache_dir: typing.Optional[str] = field(default=None)
     optim: str = field(default="adamw_torch")
     model_max_length: int = field(
         default=512,
