diff --git a/src/ImageSharp/Formats/Heif/Av1/Transform/Av1ScanOrderConstants.cs b/src/ImageSharp/Formats/Heif/Av1/Transform/Av1ScanOrderConstants.cs
index 5acac18c7f..4f7ea2d2d6 100644
--- a/src/ImageSharp/Formats/Heif/Av1/Transform/Av1ScanOrderConstants.cs
+++ b/src/ImageSharp/Formats/Heif/Av1/Transform/Av1ScanOrderConstants.cs
@@ -359,7 +359,6 @@ internal static class Av1ScanOrderConstants
     private static readonly short[] DefaultInverseScan8x8 = [];
     private static readonly short[] DefaultInverseScan16x16 = [];
     private static readonly short[] DefaultInverseScan32x32 = [];
-    private static readonly short[] DefaultInverseScan64x64 = [];
     private static readonly short[] DefaultInverseScan4x8 = [];
     private static readonly short[] DefaultInverseScan8x4 = [];
     private static readonly short[] DefaultInverseScan8x16 = [];
@@ -375,7 +374,6 @@ internal static class Av1ScanOrderConstants
     private static readonly short[] MatrixColumnInverseScan8x8 = [];
     private static readonly short[] MatrixColumnInverseScan16x16 = [];
     private static readonly short[] MatrixColumnInverseScan32x32 = [];
-    private static readonly short[] MatrixColumnInverseScan64x64 = [];
     private static readonly short[] MatrixColumnInverseScan4x8 = [];
     private static readonly short[] MatrixColumnInverseScan8x4 = [];
     private static readonly short[] MatrixColumnInverseScan8x16 = [];
@@ -391,7 +389,6 @@ internal static class Av1ScanOrderConstants
     private static readonly short[] MatrixRowInverseScan8x8 = [];
     private static readonly short[] MatrixRowInverseScan16x16 = [];
     private static readonly short[] MatrixRowInverseScan32x32 = [];
-    private static readonly short[] MatrixRowInverseScan64x64 = [];
     private static readonly short[] MatrixRowInverseScan4x8 = [];
     private static readonly short[] MatrixRowInverseScan8x4 = [];
     private static readonly short[] MatrixRowInverseScan8x16 = [];
@@ -403,12 +400,11 @@ internal static class Av1ScanOrderConstants
     private static readonly short[] MatrixRowInverseScan8x32 = [];
     private static readonly short[] MatrixRowInverseScan32x8 = [];
 
-    // Neighborss are not used (yet) for AVIF coding, leave these arrays empty for now.
+    // Neighbors are not used (yet) for AVIF coding, leave these arrays empty for now.
     private static readonly short[] DefaultScan4x4Neighbors = [];
     private static readonly short[] DefaultScan8x8Neighbors = [];
     private static readonly short[] DefaultScan16x16Neighbors = [];
     private static readonly short[] DefaultScan32x32Neighbors = [];
-    private static readonly short[] DefaultScan64x64Neighbors = [];
     private static readonly short[] DefaultScan4x8Neighbors = [];
     private static readonly short[] DefaultScan8x4Neighbors = [];
     private static readonly short[] DefaultScan8x16Neighbors = [];
@@ -424,7 +420,6 @@ internal static class Av1ScanOrderConstants
     private static readonly short[] MatrixColumnScan8x8Neighbors = [];
     private static readonly short[] MatrixColumnScan16x16Neighbors = [];
     private static readonly short[] MatrixColumnScan32x32Neighbors = [];
-    private static readonly short[] MatrixColumnScan64x64Neighbors = [];
     private static readonly short[] MatrixColumnScan4x8Neighbors = [];
     private static readonly short[] MatrixColumnScan8x4Neighbors = [];
     private static readonly short[] MatrixColumnScan8x16Neighbors = [];
@@ -440,7 +435,6 @@ internal static class Av1ScanOrderConstants
     private static readonly short[] MatrixRowScan8x8Neighbors = [];
     private static readonly short[] MatrixRowScan16x16Neighbors = [];
     private static readonly short[] MatrixRowScan32x32Neighbors = [];
-    private static readonly short[] MatrixRowScan64x64Neighbors = [];
     private static readonly short[] MatrixRowScan4x8Neighbors = [];
     private static readonly short[] MatrixRowScan8x4Neighbors = [];
     private static readonly short[] MatrixRowScan8x16Neighbors = [];
diff --git a/tests/ImageSharp.Tests/Formats/Heif/Av1/Av1CoefficientsEntropyTests.cs b/tests/ImageSharp.Tests/Formats/Heif/Av1/Av1CoefficientsEntropyTests.cs
index 8d47cbe9df..866e509a58 100644
--- a/tests/ImageSharp.Tests/Formats/Heif/Av1/Av1CoefficientsEntropyTests.cs
+++ b/tests/ImageSharp.Tests/Formats/Heif/Av1/Av1CoefficientsEntropyTests.cs
@@ -101,14 +101,14 @@ public class Av1CoefficientsEntropyTests
     }
 
     [Theory]
-    [MemberData(nameof(GetBlockSize4x4Data))]
-    public void RoundTripFullCoefficientsYSize4x4(int bSize, int txSize, int txType)
+    [MemberData(nameof(GetTransformTypes))]
+    public void RoundTripFullCoefficientsYSize4x4(int txType)
     {
         // Assign
         const ushort endOfBlock = 16;
         const Av1ComponentType componentType = Av1ComponentType.Luminance;
-        Av1BlockSize blockSize = (Av1BlockSize)bSize;
-        Av1TransformSize transformSize = (Av1TransformSize)txSize;
+        Av1BlockSize blockSize = Av1BlockSize.Block4x4;
+        Av1TransformSize transformSize = blockSize.GetMaximumTransformSize();
         Av1TransformType transformType = (Av1TransformType)txType;
         Av1PredictionMode intraDirection = Av1PredictionMode.DC;
         Av1FilterIntraMode filterIntraMode = Av1FilterIntraMode.DC;
@@ -116,14 +116,29 @@ public class Av1CoefficientsEntropyTests
     }
 
     [Theory]
-    [MemberData(nameof(GetBlockSize4x4Data))]
-    public void RoundTripFullCoefficientsUvSize4x4(int bSize, int txSize, int txType)
+    [MemberData(nameof(GetTransformTypes))]
+    public void RoundTripFullCoefficientsYSize8x8(int txType)
+    {
+        // Assign
+        const ushort endOfBlock = 16;
+        const Av1ComponentType componentType = Av1ComponentType.Luminance;
+        Av1BlockSize blockSize = Av1BlockSize.Block8x8;
+        Av1TransformSize transformSize = blockSize.GetMaximumTransformSize();
+        Av1TransformType transformType = (Av1TransformType)txType;
+        Av1PredictionMode intraDirection = Av1PredictionMode.DC;
+        Av1FilterIntraMode filterIntraMode = Av1FilterIntraMode.DC;
+        RoundTripCoefficientsCore(endOfBlock, componentType, blockSize, transformSize, transformType, intraDirection, filterIntraMode);
+    }
+
+    [Theory]
+    [MemberData(nameof(GetTransformTypes))]
+    public void RoundTripFullCoefficientsUvSize4x4(int txType)
     {
         // Assign
         const ushort endOfBlock = 16;
         const Av1ComponentType componentType = Av1ComponentType.Chroma;
-        Av1BlockSize blockSize = (Av1BlockSize)bSize;
-        Av1TransformSize transformSize = (Av1TransformSize)txSize;
+        Av1BlockSize blockSize = Av1BlockSize.Block4x4;
+        Av1TransformSize transformSize = blockSize.GetMaxUvTransformSize(true, true);
         Av1TransformType transformType = (Av1TransformType)txType;
         Av1PredictionMode intraDirection = Av1PredictionMode.DC;
         Av1FilterIntraMode filterIntraMode = Av1FilterIntraMode.DC;
@@ -155,14 +170,12 @@ public class Av1CoefficientsEntropyTests
         Assert.Equal(coefficientsBuffer[..endOfBlock], actuals[1..(endOfBlock + 1)]);
     }
 
-    public static TheoryData<int, int, int> GetBlockSize4x4Data()
+    public static TheoryData<int> GetTransformTypes()
     {
-        TheoryData<int, int, int> result = [];
-        Av1BlockSize blockSize = Av1BlockSize.Block4x4;
-        Av1TransformSize transformSize = blockSize.GetMaximumTransformSize();
+        TheoryData<int> result = [];
         for (Av1TransformType transformType = Av1TransformType.DctDct; transformType < Av1TransformType.VerticalDct; transformType++)
         {
-            result.Add((int)blockSize, (int)transformSize, (int)transformType);
+            result.Add((int)transformType);
         }
 
         return result;
diff --git a/tests/ImageSharp.Tests/Formats/Heif/Av1/Av1ScanOrderTests.cs b/tests/ImageSharp.Tests/Formats/Heif/Av1/Av1ScanOrderTests.cs
index 9844e2833c..c8c59ce21e 100644
--- a/tests/ImageSharp.Tests/Formats/Heif/Av1/Av1ScanOrderTests.cs
+++ b/tests/ImageSharp.Tests/Formats/Heif/Av1/Av1ScanOrderTests.cs
@@ -65,6 +65,45 @@ public class Av1ScanOrderTests
         Assert.Equal(width * height, scanOrder.Scan.Length);
     }
 
+    [Theory]
+    [MemberData(nameof(GetCombinations))]
+    internal void AllIndicesAreInDiagonalOrder(int s, int t)
+    {
+        // Assign
+        Av1TransformSize transformSize = (Av1TransformSize)s;
+        Av1TransformType transformType = (Av1TransformType)t;
+        int width = Math.Min(transformSize.GetWidth(), 32);
+        int height = Math.Min(transformSize.GetHeight(), 32);
+
+        // Act
+        Av1ScanOrder scanOrder = Av1ScanOrderConstants.GetScanOrder(transformSize, transformType);
+
+        // Assert
+        HashSet<int> visited = [];
+        ReadOnlySpan<short> scan = scanOrder.Scan;
+
+        // In reverse order, the indiced used in
+        // <see cref="Av1SymbolContextHelper.GetBaseRangeContext2d()" /> must already be known.
+        for (int i = scanOrder.Scan.Length - 1; i >= 0; i--)
+        {
+            visited.Add(scan[i]);
+            if (scan.Length > i + 1)
+            {
+                Assert.Contains(scan[i + 1], visited);
+            }
+
+            if (scan.Length > i + width)
+            {
+                Assert.Contains(scan[i + width], visited);
+            }
+
+            if (scan.Length > i + width + 1)
+            {
+                Assert.Contains(scan[i + width + 1], visited);
+            }
+        }
+    }
+
     public static TheoryData<int, int> GetCombinations()
     {
         TheoryData<int, int> combinations = [];