--- ./nx-X11/programs/Xserver/fb/fbtrap.c.X.original	2015-02-13 14:03:44.704442298 +0100
+++ ./nx-X11/programs/Xserver/fb/fbtrap.c	2015-02-10 19:13:14.156672722 +0100
@@ -115,6 +115,9 @@
     RenderEdge	l, r;
     xFixed	t, b;
     
+    if (!xTrapezoidValid (trap))
+	return;
+
     fbGetDrawable (pPicture->pDrawable, buf, stride, bpp, pxoff, pyoff);
 
     width = pPicture->pDrawable->width;
