diff --git a/trainer/rollout_engine.py b/trainer/rollout_engine.py
index e433a0b..3a1aab0 100644
--- a/trainer/rollout_engine.py
+++ b/trainer/rollout_engine.py
@@ -81,7 +81,7 @@ class TorchRolloutEngine(RolloutEngine):
                 num_return_sequences=1,
                 pad_token_id=self.tokenizer.pad_token_id,
                 eos_token_id=self.tokenizer.eos_token_id,
-            )  # [B*num_gen, P+R]
+            ).clone()  # [B*num_gen, P+R]
             prompt_len = prompt_ids.size(1)
             completion_ids = output_ids[:, prompt_len:]  # [B*num_gen, R]
             full_mask = (output_ids != self.tokenizer.pad_token_id).long()