diff --git a/fastNLP/modules/encoder/lstm.py b/fastNLP/modules/encoder/lstm.py
index 9bf5c628..06f8bbb7 100644
--- a/fastNLP/modules/encoder/lstm.py
+++ b/fastNLP/modules/encoder/lstm.py
@@ -70,7 +70,7 @@ class LSTM(nn.Module):
                 x = x[sort_idx]
             else:
                 x = x[:, sort_idx]
-            x = rnn.pack_padded_sequence(x, sort_lens, batch_first=self.batch_first)
+            x = rnn.pack_padded_sequence(x, sort_lens.cpu(), batch_first=self.batch_first)
             output, hx = self.lstm(x, hx)  # -> [N,L,C]
             output, _ = rnn.pad_packed_sequence(output, batch_first=self.batch_first, total_length=max_len)
             _, unsort_idx = torch.sort(sort_idx, dim=0, descending=False)