diff --git a/pong/src/geom.rs b/pong/src/geom.rs
index 5b29678..d624376 100644
--- a/pong/src/geom.rs
+++ b/pong/src/geom.rs
@@ -28,16 +28,14 @@ pub mod geom {
             self.y /= length;
         }
 
-        pub fn perpendicular_clockwise(&self) -> Vector {
-            let mut vector = Vector::new(self.y, -self.x);
-            vector.normalize();
-            vector
+        pub fn perpendicular_clockwise(&mut self) {
+            self.x = self.y;
+            self.y = -self.x;
         }
 
-        pub fn perpendicular_counter_clockwise(&self) -> Vector {
-            let mut vector = Vector::new(-self.y, self.x);
-            vector.normalize();
-            vector
+        pub fn perpendicular_counter_clockwise(&mut self) {
+            self.x = -self.y;
+            self.y = self.x;
         }
 
         pub fn add(&mut self, other: &Vector) {
diff --git a/pong/tests/vector_tests.rs b/pong/tests/vector_tests.rs
index fb8944a..c359166 100644
--- a/pong/tests/vector_tests.rs
+++ b/pong/tests/vector_tests.rs
@@ -47,11 +47,11 @@ pub fn should_calculate_angle_correctly(
 #[case(Vector::new(0., 1.), Vector::new(1., 0.))]
 #[case(Vector::new(7., 7.), Vector::new(0.7071067811865476, -0.7071067811865476))]
 pub fn should_get_perpendicular_clockwise(
-    #[case] vector: Vector,
+    #[case] mut vector: Vector,
     #[case] expected: Vector
 ) {
-    let res = vector.perpendicular_clockwise();
-    assert_eq!(res, expected);
+    vector.perpendicular_clockwise();
+    assert_eq!(vector, expected);
 }
 
 #[rstest]
@@ -59,9 +59,9 @@ pub fn should_get_perpendicular_clockwise(
 #[case(Vector::new(1., 0.), Vector::new(0., 1.))]
 #[case(Vector::new(7., 7.), Vector::new(-0.7071067811865476, 0.7071067811865476))]
 pub fn should_get_perpendicular_counter_clockwise(
-    #[case] vector: Vector,
+    #[case] mut vector: Vector,
     #[case] expected: Vector
 ) {
-    let res = vector.perpendicular_counter_clockwise();
-    assert_eq!(res, expected);
+    vector.perpendicular_counter_clockwise();
+    assert_eq!(vector, expected);
 }