diff --git a/egs/timit/ASR/tdnn_ligru_ctc/model.py b/egs/timit/ASR/tdnn_ligru_ctc/model.py
index 890f48247..64420225b 100644
--- a/egs/timit/ASR/tdnn_ligru_ctc/model.py
+++ b/egs/timit/ASR/tdnn_ligru_ctc/model.py
@@ -452,8 +452,9 @@ class LiGRU_Layer(torch.nn.Module):
                 ).data
 
             # Sampling the mask
+            left_boundary = self.drop_mask_cnt
             right_boundary = self.drop_mask_cnt + self.batch_size
-            drop_mask = self.drop_masks[self.drop_mask_cnt:right_boundary]
+            drop_mask = self.drop_masks[left_boundary:right_boundary]
             self.drop_mask_cnt = self.drop_mask_cnt + self.batch_size
 
         else: