diff --git a/src/game-lib-vector-3.js b/src/game-lib-vector-3.js
index d6396e7..6b5d802 100644
--- a/src/game-lib-vector-3.js
+++ b/src/game-lib-vector-3.js
@@ -12,6 +12,14 @@ GameLib.D3.Vector3.prototype.subtract = function (v) {
     );
 };
 
+GameLib.D3.Vector3.prototype.sub = function (v) {
+    return new GameLib.D3.Vector3(
+        this.x - v.x,
+        this.y - v.y,
+        this.z - v.z
+    );
+};
+
 GameLib.D3.Vector3.prototype.cross = function (v) {
     return new GameLib.D3.Vector3(
         this.y * v.z - this.z * v.y,
@@ -137,7 +145,7 @@ GameLib.D3.Vector3.prototype.multiply = function (s) {
             z
         );
 
-    } else if(isNumber(s)) {
+    } else if(!isNaN(parseFloat(s)) && isFinite(s)) {
 
         return new GameLib.D3.Vector3(
             this.x * s,