diff --git a/python/sglang/bench_one_batch.py b/python/sglang/bench_one_batch.py
index 69ec7c32e..a8b2e59e1 100644
--- a/python/sglang/bench_one_batch.py
+++ b/python/sglang/bench_one_batch.py
@@ -386,7 +386,7 @@ def prepare_extend_inputs_for_correctness_test(
         req.fill_ids += input_ids[i][bench_args.cut_len :]
         if model_runner is not None:
             req.prefix_indices = model_runner.req_to_token_pool.req_to_token[
-                i, : bench_args.cut_len
+                req.req_pool_idx, : bench_args.cut_len
             ].to(req.prefix_indices.dtype)
             req.logprob_start_len = -1
             req.set_extend_input_len(len(req.fill_ids) - len(req.prefix_indices))