diff --git a/step1-07/demo/src/TodoApp.tsx b/step1-07/demo/src/TodoApp.tsx
index 7c67e87..dbf9f28 100644
--- a/step1-07/demo/src/TodoApp.tsx
+++ b/step1-07/demo/src/TodoApp.tsx
@@ -53,8 +53,9 @@ export class TodoApp extends React.Component<any, any> {
   };
 
   private _complete = id => {
-    const newTodos = { ...this.state.todos };
-    newTodos[id].completed = !newTodos[id].completed;
+    const { todos } = this.state;
+    const todo = todos[id];
+    const newTodos = { ...todos, [id]: { ...todo, completed: !todo.completed } };
 
     this.setState({
       todos: newTodos
diff --git a/step1-07/exercise/src/TodoApp.tsx b/step1-07/exercise/src/TodoApp.tsx
index c8ec119..0e575cf 100644
--- a/step1-07/exercise/src/TodoApp.tsx
+++ b/step1-07/exercise/src/TodoApp.tsx
@@ -55,8 +55,9 @@ export class TodoApp extends React.Component<any, { todos: Todos; filter: Filter
   };
 
   private _complete = id => {
-    const newTodos = { ...this.state.todos };
-    newTodos[id].completed = !newTodos[id].completed;
+    const { todos } = this.state;
+    const todo = todos[id];
+    const newTodos = { ...todos, [id]: { ...todo, completed: !todo.completed } };
 
     this.setState({
       todos: newTodos
diff --git a/step1-07/final/src/TodoApp.tsx b/step1-07/final/src/TodoApp.tsx
index 6369456..1ec9fc8 100644
--- a/step1-07/final/src/TodoApp.tsx
+++ b/step1-07/final/src/TodoApp.tsx
@@ -36,8 +36,9 @@ export class TodoApp extends React.Component<{}, { todos: Todos; filter: FilterT
   };
 
   private _complete = id => {
-    const newTodos = { ...this.state.todos };
-    newTodos[id].completed = !newTodos[id].completed;
+    const { todos } = this.state;
+    const todo = todos[id];
+    const newTodos = { ...todos, [id]: { ...todo, completed: !todo.completed } };
 
     this.setState({
       todos: newTodos