diff --git a/packages/flutter/lib/src/material/checkbox.dart b/packages/flutter/lib/src/material/checkbox.dart
index b54b46e33c..ddcd1a8fbb 100644
--- a/packages/flutter/lib/src/material/checkbox.dart
+++ b/packages/flutter/lib/src/material/checkbox.dart
@@ -138,9 +138,9 @@ class Checkbox extends StatefulWidget {
   /// ```dart
   /// Checkbox(
   ///   value: _throwShotAway,
-  ///   onChanged: (bool newValue) {
+  ///   onChanged: (bool? newValue) {
   ///     setState(() {
-  ///       _throwShotAway = newValue;
+  ///       _throwShotAway = newValue!;
   ///     });
   ///   },
   /// )