Index: /trunk/src/VBox/Additions/x11/vboxvideo/vboxvideo.c
===================================================================
--- /trunk/src/VBox/Additions/x11/vboxvideo/vboxvideo.c	(revision 43270)
+++ /trunk/src/VBox/Additions/x11/vboxvideo/vboxvideo.c	(revision 43271)
@@ -1173,5 +1173,6 @@
 #endif
     /* Re-assert this in case we had a change request while switched out. */
-    VBOXAdjustScreenPixmap(pScrn, pVBox->FBSize.cx, pVBox->FBSize.cy);
+    if (pVBox->FBSize.cx && pVBox->FBSize.cy)
+        VBOXAdjustScreenPixmap(pScrn, pVBox->FBSize.cx, pVBox->FBSize.cy);
 #ifdef VBOXVIDEO_13
     if (!xf86SetDesiredModes(pScrn))