diff --git a/OpenRA.Utility/Command.cs b/OpenRA.Utility/Command.cs
index e2fa836355..196609a327 100644
--- a/OpenRA.Utility/Command.cs
+++ b/OpenRA.Utility/Command.cs
@@ -116,6 +116,8 @@ namespace OpenRA.Utility
 
 					Marshal.Copy(frame.Image, 0, data.Scan0, frame.Image.Length);
 					x += srcImage.Width;
+
+					bitmap.UnlockBits( data );
 				}
 
 				bitmap.Save(dest);