diff --git a/src/bookstore/inventory.py b/src/bookstore/inventory.py
index c295cb7..d33a236 100644
--- a/src/bookstore/inventory.py
+++ b/src/bookstore/inventory.py
@@ -29,7 +29,7 @@ class Inventory:
         """Close database connection."""
         self.conn.close()
 
-    def add(self, *books: list[Book]) -> None:
+    def add(self, *books: Book) -> None:
         """Add `Book` to the `Inventory`. `Book`s ISBN must be unique."""
         for book in books:
             try: