Index: /trunk/src/VBox/GuestHost/OpenGL/packer/pack_pixels.c
===================================================================
--- /trunk/src/VBox/GuestHost/OpenGL/packer/pack_pixels.c	(revision 42589)
+++ /trunk/src/VBox/GuestHost/OpenGL/packer/pack_pixels.c	(revision 42590)
@@ -69,5 +69,5 @@
     GLint bytes_per_row;
     int bytes_per_pixel;
-    (void)writeback;
+    *writeback = 0;
 
     bytes_per_pixel = crPixelSize(format, type);