diff --git a/packages/pinball_components/lib/src/components/bumping_behavior.dart b/packages/pinball_components/lib/src/components/bumping_behavior.dart
index ab2ee28e..654f96b4 100644
--- a/packages/pinball_components/lib/src/components/bumping_behavior.dart
+++ b/packages/pinball_components/lib/src/components/bumping_behavior.dart
@@ -6,10 +6,10 @@ import 'package:pinball_flame/pinball_flame.dart';
 /// {@endtemplate}
 class BumpingBehavior extends ContactBehavior {
   /// {@macro bumping_behavior}
-  BumpingBehavior({required this.strength});
+  BumpingBehavior({required double strength}) : _strength = strength;
 
   /// Determines how strong the bump is.
-  double strength;
+  final double _strength;
 
   @override
   void postSolve(Object other, Contact contact, ContactImpulse impulse) {
@@ -19,7 +19,7 @@ class BumpingBehavior extends ContactBehavior {
     other.body.applyLinearImpulse(
       contact.manifold.localPoint
         ..normalize()
-        ..multiply(Vector2.all(other.body.mass * strength)),
+        ..multiply(Vector2.all(other.body.mass * _strength)),
     );
   }
 }
diff --git a/packages/pinball_components/test/src/components/bumping_behavior_test.dart b/packages/pinball_components/test/src/components/bumping_behavior_test.dart
index 8d1d533d..d346a0ae 100644
--- a/packages/pinball_components/test/src/components/bumping_behavior_test.dart
+++ b/packages/pinball_components/test/src/components/bumping_behavior_test.dart
@@ -58,7 +58,6 @@ void main() {
           dummy2,
         ]);
 
-        expect(behavior2.strength, greaterThan(behavior1.strength));
         expect(dummy1.body.inverseMass, greaterThan(0));
         expect(dummy2.body.inverseMass, greaterThan(0));