diff --git a/Source/OpenTK/Math/Matrix3.cs b/Source/OpenTK/Math/Matrix3.cs
index cd2f3bc7..18b5c6fb 100644
--- a/Source/OpenTK/Math/Matrix3.cs
+++ b/Source/OpenTK/Math/Matrix3.cs
@@ -667,7 +667,25 @@ namespace OpenTK
         }
         
         #endregion
-        
+
+        #region Add Functions
+
+        public static Matrix3 Add(Matrix3 left, Matrix3 right)
+        {
+            Matrix3 result;
+            Add(ref left, ref right, out result);
+            return result;
+        }
+
+        public static void Add(ref Matrix3 left, ref Matrix3 right, out Matrix3 result)
+        {
+            Vector3.Add(ref left.Row0, ref right.Row0, out result.Row0);
+            Vector3.Add(ref left.Row1, ref right.Row1, out result.Row1);
+            Vector3.Add(ref left.Row2, ref right.Row2, out result.Row2);
+        }
+
+        #endregion
+
         #region Multiply Functions
 
         /// <summary>
diff --git a/Source/OpenTK/Math/Matrix3d.cs b/Source/OpenTK/Math/Matrix3d.cs
index 757c36ca..79633534 100644
--- a/Source/OpenTK/Math/Matrix3d.cs
+++ b/Source/OpenTK/Math/Matrix3d.cs
@@ -664,7 +664,25 @@ namespace OpenTK
         }
         
         #endregion
-        
+
+        #region Add Functions
+
+        public static Matrix3d Add(Matrix3d left, Matrix3d right)
+        {
+            Matrix3d result;
+            Add(ref left, ref right, out result);
+            return result;
+        }
+
+        public static void Add(ref Matrix3d left, ref Matrix3d right, out Matrix3d result)
+        {
+            Vector3d.Add(ref left.Row0, ref right.Row0, out result.Row0);
+            Vector3d.Add(ref left.Row1, ref right.Row1, out result.Row1);
+            Vector3d.Add(ref left.Row2, ref right.Row2, out result.Row2);
+        }
+
+        #endregion
+
         #region Multiply Functions
 
         /// <summary>
diff --git a/Source/OpenTK/Math/Matrix4.cs b/Source/OpenTK/Math/Matrix4.cs
index 2d311fd5..945f367d 100644
--- a/Source/OpenTK/Math/Matrix4.cs
+++ b/Source/OpenTK/Math/Matrix4.cs
@@ -117,6 +117,30 @@ namespace OpenTK
             Row3 = new Vector4(m30, m31, m32, m33);
         }
 
+        /// <summary>
+        /// Constructs a new instance.
+        /// </summary>
+        /// <param name="topLeft">The top left 3x3 of the matrix.</param>
+        public Matrix4(Matrix3 topLeft)
+        {
+            Row0.X = topLeft.Row0.X;
+            Row0.Y = topLeft.Row0.Y;
+            Row0.Z = topLeft.Row0.Z;
+            Row0.W = 0;
+            Row1.X = topLeft.Row1.X;
+            Row1.Y = topLeft.Row1.Y;
+            Row1.Z = topLeft.Row1.Z;
+            Row1.W = 0;
+            Row2.X = topLeft.Row2.X;
+            Row2.Y = topLeft.Row2.Y;
+            Row2.Z = topLeft.Row2.Z;
+            Row2.W = 0;
+            Row3.X = 0;
+            Row3.Y = 0;
+            Row3.Z = 0;
+            Row3.W = 1;
+        }
+
         #endregion
 
         #region Public Members
diff --git a/Source/OpenTK/Math/Matrix4d.cs b/Source/OpenTK/Math/Matrix4d.cs
index 785a6a12..8a2a2137 100644
--- a/Source/OpenTK/Math/Matrix4d.cs
+++ b/Source/OpenTK/Math/Matrix4d.cs
@@ -109,6 +109,30 @@ namespace OpenTK
             Row3 = new Vector4d(m30, m31, m32, m33);
         }
 
+        /// <summary>
+        /// Constructs a new instance.
+        /// </summary>
+        /// <param name="topLeft">The top left 3x3 of the matrix.</param>
+        public Matrix4d(Matrix3d topLeft)
+        {
+            Row0.X = topLeft.Row0.X;
+            Row0.Y = topLeft.Row0.Y;
+            Row0.Z = topLeft.Row0.Z;
+            Row0.W = 0;
+            Row1.X = topLeft.Row1.X;
+            Row1.Y = topLeft.Row1.Y;
+            Row1.Z = topLeft.Row1.Z;
+            Row1.W = 0;
+            Row2.X = topLeft.Row2.X;
+            Row2.Y = topLeft.Row2.Y;
+            Row2.Z = topLeft.Row2.Z;
+            Row2.W = 0;
+            Row3.X = 0;
+            Row3.Y = 0;
+            Row3.Z = 0;
+            Row3.W = 1;
+        }
+
         #endregion
 
         #region Public Members