diff --git a/content/pong/scoring/ball_respawn.md b/content/pong/scoring/ball_respawn.md
index 5293cd2..24e1eac 100644
--- a/content/pong/scoring/ball_respawn.md
+++ b/content/pong/scoring/ball_respawn.md
@@ -66,6 +66,17 @@ While we're at it, let's add a few more math helper functions.
     }
 ```
 
+We need one last utility function. Bizarrely, **Vector2** does not provide a built-in rotation function. Let's fix that.
+
+In **Vector2Extensions.cs**:
+
+```cs
+    public static Vector2 Rotate(this Vector2 vector, float radians)
+    {
+        return Vector2.Transform(vector, Matrix3x2.CreateRotation(radians));
+    }
+```
+
 Now we can construct a formula for our random serve direction. First, let's change the BallSpawner to take a speed value instead of a specific velocity.
 
 {{% notice tip %}}
@@ -90,8 +101,8 @@ The difference between speed and velocity is that velocity contains directional
 Now, in **BallSpawner.cs**:
 
 ```cs
-    var direction = (float)MathHelper.RandomDouble(-System.Math.PI / 4.0, System.Math.PI / 4.0);
-    var velocity = new Vector2(message.Speed * (MathHelper.CoinFlip() ? -1 : 1), 0).Rotate(direction);
+    var direction = MathHelper.RandomDouble(-System.Math.PI / 4.0, System.Math.PI / 4.0);
+    var velocity = new Vector2(message.Speed * (MathHelper.CoinFlip() ? -1 : 1), 0).Rotate((float)direction);
     AddComponent(ball, new VelocityComponent(velocity));
 ```