diff --git a/wenet/models/firered/subsampling.py b/wenet/models/firered/subsampling.py
index d4e98ea91..a426b3431 100644
--- a/wenet/models/firered/subsampling.py
+++ b/wenet/models/firered/subsampling.py
@@ -64,8 +64,13 @@ def forward(
         x_lens = torch.sum(x_mask.squeeze(1), dim=1)
         x_lens = x_lens + self.right_context
         x_mask = make_non_pad_mask(x_lens).unsqueeze(1)
+        mask_seq = x_mask.size(2)
         x = torch.nn.functional.pad(x, (0, 0, 0, self.right_context),
                                     'constant', 0.0)
+        x_seq = x.size(1)
+        if x_seq > mask_seq:
+            x_mask = torch.nn.functional.pad(x_mask, (0, x_seq - mask_seq, 0,0,0,0),'constant', 0.0)
+
         x = x.unsqueeze(1)  # (b, c=1, t, f)
         x = self.conv(x)
         b, c, t, f = x.size()