diff --git a/src/ImageSharp/Processing/AffineTransformBuilder.cs b/src/ImageSharp/Processing/AffineTransformBuilder.cs
index 51a110dfc..c7007679f 100644
--- a/src/ImageSharp/Processing/AffineTransformBuilder.cs
+++ b/src/ImageSharp/Processing/AffineTransformBuilder.cs
@@ -268,6 +268,9 @@ namespace SixLabors.ImageSharp.Processing
         /// Returns the combined matrix for a given source rectangle.
         /// </summary>
         /// <param name="sourceRectangle">The rectangle in the source image.</param>
+        /// <exception cref="DegenerateTransformException">
+        /// The resultant matrix contains one or more values equivalent to <see cref="float.NaN"/>.
+        /// </exception>
         /// <returns>The <see cref="Matrix3x2"/>.</returns>
         public Matrix3x2 BuildMatrix(Rectangle sourceRectangle)
         {
diff --git a/src/ImageSharp/Processing/ProjectiveTransformBuilder.cs b/src/ImageSharp/Processing/ProjectiveTransformBuilder.cs
index caebc34a3..a407074aa 100644
--- a/src/ImageSharp/Processing/ProjectiveTransformBuilder.cs
+++ b/src/ImageSharp/Processing/ProjectiveTransformBuilder.cs
@@ -284,6 +284,9 @@ namespace SixLabors.ImageSharp.Processing
         /// Returns the combined matrix for a given source rectangle.
         /// </summary>
         /// <param name="sourceRectangle">The rectangle in the source image.</param>
+        /// <exception cref="DegenerateTransformException">
+        /// The resultant matrix contains one or more values equivalent to <see cref="float.NaN"/>.
+        /// </exception>
         /// <returns>The <see cref="Matrix4x4"/>.</returns>
         public Matrix4x4 BuildMatrix(Rectangle sourceRectangle)
         {