diff --git a/demo/inference_img.py b/demo/inference_img.py
index e9e1647..6e4a8fe 100644
--- a/demo/inference_img.py
+++ b/demo/inference_img.py
@@ -259,7 +259,7 @@ def _inference_one(img, maskdts, curr_mask, target_class, out_writer): # to save
     parser.add_argument('--video', required=True, help='path to the rgb video')
     parser.add_argument('--masks_video', required=True, help='path to the video with masks')
     parser.add_argument('--out_video', required=True, help='path to the output video with masks')
-    parser.add_argument('--target_class', required=False, default=None, help='mark of the target semantic class')
+    parser.add_argument('--target_class', required=False, default=None, type=int, help='mark of the target semantic class')
 
     args = parser.parse_args()