diff --git a/fe/bench/workload.py b/fe/bench/workload.py
index ff89430..57c3648 100644
--- a/fe/bench/workload.py
+++ b/fe/bench/workload.py
@@ -92,7 +92,7 @@ class Workload:
                     for bk in books:
                         code = seller.add_book(store_id, self.stock_level, bk)
                         assert code == 200
-                        self.book_ids[store_ids].append(bk.id)
+                        self.book_ids[store_id].append(bk.id)
                     row_no = row_no + len(books)
         logging.info("seller data loaded.")
         for k in range(1, self.buyer_num + 1):