diff --git a/egs/librispeech/ASR/pruned_transducer_stateless7/zipformer.py b/egs/librispeech/ASR/pruned_transducer_stateless7/zipformer.py
index 0a25ca8f4..2c215f0f1 100644
--- a/egs/librispeech/ASR/pruned_transducer_stateless7/zipformer.py
+++ b/egs/librispeech/ASR/pruned_transducer_stateless7/zipformer.py
@@ -292,7 +292,14 @@ class Zipformer2(EncoderInterface):
 
         assert self.encoder_dim[0] == _encoder_dims0
 
-        max_downsampling_factor = max(self.downsampling_factor)
+
+        # this is a heuristic, the regions over which we masked frames are 4 times the
+        # largest of the downsampling_factors.  Can be any integer >= 1.
+        downsampling_multiple = 4
+
+        downsampling_factor = [ downsampling_multiple * i for i in self.downsampling_factor ]
+
+        max_downsampling_factor = max(downsampling_factor)
 
         num_frames_max = (num_frames0 + max_downsampling_factor - 1)
 
@@ -318,7 +325,7 @@ class Zipformer2(EncoderInterface):
 
         feature_masks = []
         for i in range(num_encoders):
-            ds = self.downsampling_factor[i]
+            ds = downsampling_factor[i]
             upsample_factor = (max_downsampling_factor // ds)
 
             frame_mask = (frame_mask_max.unsqueeze(1).expand(num_frames_max, upsample_factor,