diff --git a/src/math/Matrix3.js b/src/math/Matrix3.js
index 898522dfd6ae2e..5e954214902eae 100644
--- a/src/math/Matrix3.js
+++ b/src/math/Matrix3.js
@@ -2,7 +2,7 @@ class Matrix3 {
 
 	constructor() {
 
-		this.isMatrix3 = true;
+		Matrix3.prototype.isMatrix3 = true;
 
 		this.elements = [
 
diff --git a/src/math/Matrix4.js b/src/math/Matrix4.js
index 70a69393932cc7..42aff06efbecb8 100644
--- a/src/math/Matrix4.js
+++ b/src/math/Matrix4.js
@@ -4,7 +4,7 @@ class Matrix4 {
 
 	constructor() {
 
-		this.isMatrix4 = true;
+		Matrix4.prototype.isMatrix4 = true;
 
 		this.elements = [
 
diff --git a/src/math/Vector2.js b/src/math/Vector2.js
index 8000533a7c1f3e..4a229857bde796 100644
--- a/src/math/Vector2.js
+++ b/src/math/Vector2.js
@@ -2,7 +2,7 @@ class Vector2 {
 
 	constructor( x = 0, y = 0 ) {
 
-		this.isVector2 = true;
+		Vector2.prototype.isVector2 = true;
 
 		this.x = x;
 		this.y = y;
diff --git a/src/math/Vector3.js b/src/math/Vector3.js
index 7ca8d06d823fd1..9a8545e04370b2 100644
--- a/src/math/Vector3.js
+++ b/src/math/Vector3.js
@@ -5,7 +5,7 @@ class Vector3 {
 
 	constructor( x = 0, y = 0, z = 0 ) {
 
-		this.isVector3 = true;
+		Vector3.prototype.isVector3 = true;
 
 		this.x = x;
 		this.y = y;
diff --git a/src/math/Vector4.js b/src/math/Vector4.js
index d2edcf22df7db9..c5613d5a56dc85 100644
--- a/src/math/Vector4.js
+++ b/src/math/Vector4.js
@@ -2,7 +2,7 @@ class Vector4 {
 
 	constructor( x = 0, y = 0, z = 0, w = 1 ) {
 
-		this.isVector4 = true;
+		Vector4.prototype.isVector4 = true;
 
 		this.x = x;
 		this.y = y;
diff --git a/test/unit/src/core/Object3D.tests.js b/test/unit/src/core/Object3D.tests.js
index a5330cb1971662..dc624d08bfa0d5 100644
--- a/test/unit/src/core/Object3D.tests.js
+++ b/test/unit/src/core/Object3D.tests.js
@@ -301,9 +301,11 @@ export default QUnit.module( 'Core', () => {
 			obj.translateOnAxis( new Vector3( 0, 1, 0 ), 1.23 );
 			obj.translateOnAxis( new Vector3( 0, 0, 1 ), - 4.56 );
 
-			assert.numEqual( obj.position.x, 1, 'x is equal' );
-			assert.numEqual( obj.position.y, 1.23, 'y is equal' );
-			assert.numEqual( obj.position.z, - 4.56, 'z is equal' );
+			assert.propEqual( obj.position, {
+				x: 1,
+				y: 1.23,
+				z: - 4.56,
+			} );
 
 		} );