diff --git a/isc.py b/isc.py
index f70f5c4..8a5ee07 100644
--- a/isc.py
+++ b/isc.py
@@ -86,8 +86,8 @@ class Isc(NNOperator):
                                  std=self.backbone.default_cfg['std'])
         ])
 
-    def __call__(self, data: Union[List[towhee._types.Image], towhee._types.Image]):
-        if isinstance(data, towhee._types.Image):
+    def __call__(self, data: Union[List['towhee.types.Image'], 'towhee.types.Image']):
+        if not isinstance(data, list):
             imgs = [data]
         else:
             imgs = data