diff --git a/OpenRA.Mods.Common/UtilityCommands/ConvertSpriteToPngCommand.cs b/OpenRA.Mods.Common/UtilityCommands/ConvertSpriteToPngCommand.cs
index 9306108d31b7..d2d1fa4f1f93 100644
--- a/OpenRA.Mods.Common/UtilityCommands/ConvertSpriteToPngCommand.cs
+++ b/OpenRA.Mods.Common/UtilityCommands/ConvertSpriteToPngCommand.cs
@@ -71,11 +71,14 @@ void IUtilityCommand.Run(Utility utility, string[] args)
 				var pngData = frame.Data;
 				if (frameSize != frame.Size)
 				{
+					var width = Math.Min(frame.Size.Width, frameSize.Width - offset.X);
+					var height = Math.Min(frame.Size.Height, frameSize.Height - offset.Y);
 					pngData = new byte[frameSize.Width * frameSize.Height];
-					for (var i = 0; i < frame.Size.Height; i++)
-						Buffer.BlockCopy(frame.Data, i * frame.Size.Width,
-							pngData, (i + offset.Y) * frameSize.Width + offset.X,
-							frame.Size.Width);
+					for (var h = 0; h < height; h++)
+						Array.Copy(
+							frame.Data, h * frame.Size.Width,
+							pngData, (h + offset.Y) * frameSize.Width + offset.X,
+							width);
 				}
 
 				var png = new Png(pngData, SpriteFrameType.Indexed8, frameSize.Width, frameSize.Height, palColors);