diff --git a/egs/librispeech/SSL/zipformer/hubert_ce.py b/egs/librispeech/SSL/zipformer/hubert_ce.py
index 1d9fd31f9..4a6b770df 100644
--- a/egs/librispeech/SSL/zipformer/hubert_ce.py
+++ b/egs/librispeech/SSL/zipformer/hubert_ce.py
@@ -429,7 +429,7 @@ class HubertModel(nn.Module):
         # padding_mask: (B, T), bool
         # mask_indices: (B, T), bool
         x = x.transpose(0, 1)
-        x, x_lens = self.encoder(x, (~padding_mask).sum(dim=-1) if padding_mask else None)
+        x, x_lens = self.encoder(x, (~padding_mask).sum(dim=-1) if padding_mask is not None else None)
         x = x.transpose(0, 1)
 
         if features_only: