diff --git a/isc.py b/isc.py
index 3948aa4..158a0a9 100644
--- a/isc.py
+++ b/isc.py
@@ -174,7 +174,7 @@ class Isc(NNOperator):
         return path
 
     @arg(1, to_image_color('RGB'))
-    def convert_img(self, img: towhee._types.Image):
+    def convert_img(self, img: 'towhee.types.Image'):
         img = PILImage.fromarray(img.astype('uint8'), 'RGB')
         return img