diff --git a/src/Oh.My.Stitcher/Tile.cs b/src/Oh.My.Stitcher/Tile.cs
index bba9651..66df0b3 100644
--- a/src/Oh.My.Stitcher/Tile.cs
+++ b/src/Oh.My.Stitcher/Tile.cs
@@ -17,6 +17,8 @@ public static class Tile
   {
     if( !TryParseRect(request.CanvasRect, out int minRow, out int maxRow, out int minCol, out int maxCol) )
       throw new ArgumentException($"Invalid canvas_rect: '{request.CanvasRect}'");
+    if( maxRow > byte.MaxValue || maxCol > byte.MaxValue )
+      throw new NotSupportedException($"Unsupported rect row: {maxRow}, col: {maxCol}");
 
     logger.ZLogDebug(
       $"rect: {request.CanvasRect}, minRow: {minRow}, maxRow: {maxRow}, minCol: {minCol}, maxCol: {maxCol}");
@@ -38,16 +40,20 @@ public static class Tile
     bool canBeCached = ( predictedW * predictedH ) <= MAX_CACHED_TILE_SIZE;
     if( canBeCached )
     {
-      Span<byte> buffer = stackalloc byte[36];
-      MemoryMarshal.Write(buffer, in minRow);
-      MemoryMarshal.Write(buffer[4..], in maxRow);
-      MemoryMarshal.Write(buffer[8..], in minCol);
-      MemoryMarshal.Write(buffer[12..], in maxCol);
-      MemoryMarshal.Write(buffer[16..], in cropOffsetX);
-      MemoryMarshal.Write(buffer[20..], in cropOffsetY);
-      MemoryMarshal.Write(buffer[24..], in cropSizeW);
-      MemoryMarshal.Write(buffer[28..], in cropSizeH);
-      MemoryMarshal.Write(buffer[32..], in outputScale);
+      Span<byte> buffer = stackalloc byte[24];
+      byte minRowByte = (byte)minRow;
+      byte maxRowByte = (byte)maxRow;
+      byte minColByte = (byte)minCol;
+      byte maxColByte = (byte)maxCol;
+      MemoryMarshal.Write(buffer, in minRowByte);
+      MemoryMarshal.Write(buffer[1..], in maxRowByte);
+      MemoryMarshal.Write(buffer[2..], in minColByte);
+      MemoryMarshal.Write(buffer[3..], in maxColByte);
+      MemoryMarshal.Write(buffer[4..], in cropOffsetX);
+      MemoryMarshal.Write(buffer[8..], in cropOffsetY);
+      MemoryMarshal.Write(buffer[12..], in cropSizeW);
+      MemoryMarshal.Write(buffer[16..], in cropSizeH);
+      MemoryMarshal.Write(buffer[20..], in outputScale);
       cacheKey = Convert.ToHexString(buffer).ToLowerInvariant();
       if( cache.TryGetValue(cacheKey, out cacheFile) && File.Exists(cacheFile) )
         return false;