diff --git a/Source/OpenTK/Math/Vector3.cs b/Source/OpenTK/Math/Vector3.cs
index 596fa0eb..03eb1328 100644
--- a/Source/OpenTK/Math/Vector3.cs
+++ b/Source/OpenTK/Math/Vector3.cs
@@ -35,10 +35,12 @@ namespace OpenTK.Math
 		/// </summary>
 		public float Z;
 
-		public static Vector3 UnitX = new Vector3(1, 0, 0);
-		public static Vector3 UnitY = new Vector3(0, 1, 0);
-		public static Vector3 UnitZ = new Vector3(0, 0, 1);
-		public static Vector3 Zero = new Vector3(0, 0, 0);
+        public static readonly Vector3 UnitX = new Vector3(1, 0, 0);
+        public static readonly Vector3 UnitY = new Vector3(0, 1, 0);
+        public static readonly Vector3 UnitZ = new Vector3(0, 0, 1);
+        public static readonly Vector3 Zero = new Vector3(0, 0, 0);
+
+        public static readonly int SizeInBytes = Marshal.SizeOf(new Vector3());
 
         #endregion