diff --git a/src/ImageSharp/Processing/Processors/Quantization/EuclideanPixelMap{TPixel}.cs b/src/ImageSharp/Processing/Processors/Quantization/EuclideanPixelMap{TPixel}.cs
index b82ce71bb..f54489348 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/EuclideanPixelMap{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/EuclideanPixelMap{TPixel}.cs
@@ -22,7 +22,9 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
         where TPixel : unmanaged, IPixel<TPixel>
     {
         private Rgba32[] rgbaPalette;
-        private readonly ColorDistanceCache cache;
+
+        // Do not make this readonly! Struct value would be always copied on non-readonly method calls.
+        private ColorDistanceCache cache;
         private readonly Configuration configuration;
 
         /// <summary>