diff --git a/step1-07/demo/src/TodoApp.types.ts b/step1-07/demo/src/TodoApp.types.ts
index fb42585..9497598 100644
--- a/step1-07/demo/src/TodoApp.types.ts
+++ b/step1-07/demo/src/TodoApp.types.ts
@@ -1,6 +1,6 @@
 export type FilterTypes = 'all' | 'active' | 'completed';
 
-export type CompleteTodo = (id) => null;
+export type CompleteTodo = (id) => void;
 
 export interface TodoItem {
   label: string;