diff --git a/src/dataset.py b/src/dataset.py
index 001424cb5dfce365c3a6df11353412e6ad196d78..e65c312c3f2b3ba12533194d55f7e4446f1396ce 100644
--- a/src/dataset.py
+++ b/src/dataset.py
@@ -305,7 +305,7 @@ class RMDataset(Dataset):
 
     def __getitem__(self, index):
         ctx_len = self.args.ctx_len
-        req_len = ctx_len + 1
+        req_len = ctx_len
         prompt_prefer_idx, prompt_alter_idx, prompt_prefer_mask, prompt_alter_mask = self.data[index]
 
         prompt_prefer_idx = prompt_prefer_idx[: req_len]