diff --git a/lib/src/custom_matcher.dart b/lib/src/custom_matcher.dart
index 862d133..43ccaa9 100644
--- a/lib/src/custom_matcher.dart
+++ b/lib/src/custom_matcher.dart
@@ -21,7 +21,7 @@
 /// ```dart
 /// class HasPrice extends CustomMatcher {
 ///   HasPrice(matcher) : super("Widget with price that is", "price", matcher);
-///   featureValueOf(actual) => actual.price;
+///   featureValueOf(actual) => (actual as Widget).price;
 /// }
 /// ```
 ///
diff --git a/test/custom_matcher_test.dart b/test/custom_matcher_test.dart
index 53f035b..537679c 100644
--- a/test/custom_matcher_test.dart
+++ b/test/custom_matcher_test.dart
@@ -14,7 +14,7 @@
 
 class _HasPrice extends CustomMatcher {
   _HasPrice(matcher) : super("Widget with a price that is", "price", matcher);
-  Object featureValueOf(actual) => actual.price;
+  Object featureValueOf(actual) => (actual as Widget).price;
 }
 
 void main() {