diff --git a/lhotse/cut/set.py b/lhotse/cut/set.py
index 09789f67f..977438e82 100644
--- a/lhotse/cut/set.py
+++ b/lhotse/cut/set.py
@@ -2874,7 +2874,10 @@ def compute_supervisions_frame_mask(
                     if ali.end < cut.duration
                     else num_frames
                 )
+                if et <= 0:
+                    continue
                 mask[st:et] = 1.0
+
         else:
             st = round(supervision.start / frame_shift) if supervision.start > 0 else 0
             et = (
@@ -2882,7 +2885,10 @@ def compute_supervisions_frame_mask(
                 if supervision.end < cut.duration
                 else num_frames
             )
+            if et <= 0:
+                continue
             mask[st:et] = 1.0
+
     return mask