diff --git a/icefall/.utils.py.swp b/icefall/.utils.py.swp
index f8ddcd2ba..e89cb8a34 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 5186e33ac..7eb780a74 100644
--- a/icefall/utils.py
+++ b/icefall/utils.py
@@ -205,12 +205,12 @@ def encode_supervisions(
         (
             supervisions["sequence_idx"],
             torch.div(
-                num_frames
+                start_frame,
                 subsampling_factor,
                 rounding_mode="floor",
             ),
             torch.div(
-                supervisions["num_frames"],
+                num_frames,
                 subsampling_factor,
                 rounding_mode="floor",
             ),