--- sys/dev/e1000/if_igb.c	2008-11-22 14:39:42.000000000 +0800
+++ /var/current/mysrc/sys/dev/e1000/if_igb.c	2008-11-25 11:51:34.000000000 +0800
@@ -3494,7 +3494,8 @@
 	 * 'j' is the failing index, decrement it to get the
 	 * last success.
 	 */
-	for (--j; j < 0; j--) {
+	j--;
+	for (; j >= 0; j--) {
 		rxbuf = &rxr->rx_buffers[j];
 		if (rxbuf->m_head != NULL) {
 			bus_dmamap_sync(rxr->rxtag, rxbuf->map,