diff --git a/src/i830_dri.c b/src/i830_dri.c
index 9da1d40..23f45a5 100644
--- a/src/i830_dri.c
+++ b/src/i830_dri.c
@@ -325,8 +325,9 @@ I830DRI2CopyRegion(DrawablePtr pDraw, RegionPtr pRegion,
 		load_scan_lines_pipe = MI_LOAD_SCAN_LINES_DISPLAY_PIPEB;
 	    }
 
-	    y1 = box->y1 - crtc->y;
-	    y2 = box->y2 - crtc->y;
+	    //calculate scan line numbers 
+	    y1 = (crtcbox->y1 <= box->y1) ? box->y1 - crtcbox->y1 : 0;
+	    y2 = (box->y2 <= crtcbox->y2) ? box->y2 - crtcbox->y1 : crtcbox->y2 - crtcbox->y1;
 
 	    BEGIN_BATCH(5);
 	    /* The documentation says that the LOAD_SCAN_LINES command