diff --git a/data/part-10/4-application-development.md b/data/part-10/4-application-development.md
index c5607e01..d5e669aa 100644
--- a/data/part-10/4-application-development.md
+++ b/data/part-10/4-application-development.md
@@ -807,9 +807,9 @@ This removes an _unnecessary dependency_ from the `PhoneBookApplication` class.
 
 ```python
 class PhoneBookApplication:
-    def __init__(self, filename):
+    def __init__(self, storage_service):
         self.__phonebook = PhoneBook()
-        self.__filename = filename
+        self.__storage_service = storage_service
 
     # the rest of the user interface