diff --git a/src/ImageSharp/Formats/WebP/Lossless/LosslessUtils.cs b/src/ImageSharp/Formats/WebP/Lossless/LosslessUtils.cs
index ac69906652..e8dd3c40a4 100644
--- a/src/ImageSharp/Formats/WebP/Lossless/LosslessUtils.cs
+++ b/src/ImageSharp/Formats/WebP/Lossless/LosslessUtils.cs
@@ -261,7 +261,7 @@ namespace SixLabors.ImageSharp.Formats.WebP.Lossless
 
                 // First Row follows the L (mode=1) mode.
                 PredictorAdd0(input, null, 1, output);
-                PredictorAdd1(input + 1, null, width - 1, output);
+                PredictorAdd1(input + 1, null, width - 1, output + 1);
                 input += width;
                 output += width;