diff --git a/lib/cyberarm_engine/vector.rb b/lib/cyberarm_engine/vector.rb
index 7fef61e..f601ea1 100644
--- a/lib/cyberarm_engine/vector.rb
+++ b/lib/cyberarm_engine/vector.rb
@@ -143,7 +143,7 @@ module CyberarmEngine
       x = @x * e[0]  + @y * e[1]  + @z * e[2]  + 1 * e[3]
       y = @x * e[4]  + @y * e[5]  + @z * e[6]  + 1 * e[7]
       z = @x * e[8]  + @y * e[9]  + @z * e[10] + 1 * e[11]
-      w = @x * e[12] + @y * e[13] + @z * e[14] + 1 * e[5]
+      w = @x * e[12] + @y * e[13] + @z * e[14] + 1 * e[15]
 
       Vector.new(x / 1, y / 1, z / 1, w / 1)
     end