diff --git a/icefall/.utils.py.swp b/icefall/.utils.py.swp
index b8aeeea90..f8ddcd2ba 100644
Binary files a/icefall/.utils.py.swp and b/icefall/.utils.py.swp differ
diff --git a/icefall/utils.py b/icefall/utils.py
index c9dec476c..5186e33ac 100644
--- a/icefall/utils.py
+++ b/icefall/utils.py
@@ -205,7 +205,7 @@ def encode_supervisions(
         (
             supervisions["sequence_idx"],
             torch.div(
-                supervisions["start_frame"],
+                num_frames
                 subsampling_factor,
                 rounding_mode="floor",
             ),