diff --git a/fastNLP/modules/decoder/CRF.py b/fastNLP/modules/decoder/CRF.py
index a15f2175..91064da2 100644
--- a/fastNLP/modules/decoder/CRF.py
+++ b/fastNLP/modules/decoder/CRF.py
@@ -16,7 +16,7 @@ def seq_len_to_byte_mask(seq_lens):
     batch_size = seq_lens.size(0)
     max_len = seq_lens.max()
     broadcast_arange = torch.arange(max_len).view(1, -1).repeat(batch_size, 1).to(seq_lens.device)
-    mask = broadcast_arange.lt(seq_lens.float().view(-1, 1))
+    mask = broadcast_arange.float().lt(seq_lens.float().view(-1, 1))
     return mask
 
 def allowed_transitions(id2label, encoding_type='bio'):