diff --git a/Source/OpenTK/Math/Matrix3.cs b/Source/OpenTK/Math/Matrix3.cs
index 18b5c6fb..9d720c8c 100644
--- a/Source/OpenTK/Math/Matrix3.cs
+++ b/Source/OpenTK/Math/Matrix3.cs
@@ -670,6 +670,12 @@ namespace OpenTK
 
         #region Add Functions
 
+        /// <summary>
+        /// Adds two instances.
+        /// </summary>
+        /// <param name="left">The left operand of the addition.</param>
+        /// <param name="right">The right operand of the addition.</param>
+        /// <returns>A new instance that is the result of the addition.</returns>
         public static Matrix3 Add(Matrix3 left, Matrix3 right)
         {
             Matrix3 result;
@@ -677,6 +683,12 @@ namespace OpenTK
             return result;
         }
 
+        /// <summary>
+        /// Adds two instances.
+        /// </summary>
+        /// <param name="left">The left operand of the addition.</param>
+        /// <param name="right">The right operand of the addition.</param>
+        /// <param name="result">A new instance that is the result of the addition.</param>
         public static void Add(ref Matrix3 left, ref Matrix3 right, out Matrix3 result)
         {
             Vector3.Add(ref left.Row0, ref right.Row0, out result.Row0);
diff --git a/Source/OpenTK/Math/Matrix3d.cs b/Source/OpenTK/Math/Matrix3d.cs
index 79633534..ca270b8a 100644
--- a/Source/OpenTK/Math/Matrix3d.cs
+++ b/Source/OpenTK/Math/Matrix3d.cs
@@ -667,6 +667,12 @@ namespace OpenTK
 
         #region Add Functions
 
+        /// <summary>
+        /// Adds two instances.
+        /// </summary>
+        /// <param name="left">The left operand of the addition.</param>
+        /// <param name="right">The right operand of the addition.</param>
+        /// <returns>A new instance that is the result of the addition.</returns>
         public static Matrix3d Add(Matrix3d left, Matrix3d right)
         {
             Matrix3d result;
@@ -674,6 +680,12 @@ namespace OpenTK
             return result;
         }
 
+        /// <summary>
+        /// Adds two instances.
+        /// </summary>
+        /// <param name="left">The left operand of the addition.</param>
+        /// <param name="right">The right operand of the addition.</param>
+        /// <param name="result">A new instance that is the result of the addition.</param>
         public static void Add(ref Matrix3d left, ref Matrix3d right, out Matrix3d result)
         {
             Vector3d.Add(ref left.Row0, ref right.Row0, out result.Row0);