diff --git a/vllm/transformers_utils/detokenizer.py b/vllm/transformers_utils/detokenizer.py
index 345ea14f..7c8423d2 100644
--- a/vllm/transformers_utils/detokenizer.py
+++ b/vllm/transformers_utils/detokenizer.py
@@ -90,7 +90,7 @@ class Detokenizer:
             prefix_offset = next_iter_prefix_offset
             read_offset = next_iter_read_offset
             if prev_tokens is None:
-                prev_tokens = next_iter_tokens
+                prev_tokens = next_iter_tokens.copy()
             else:
                 prev_tokens.extend(next_iter_tokens)