diff -urp nmap-3.78/scan_engine.cc nmap-3.78mm/scan_engine.cc
--- nmap-3.78/scan_engine.cc	2004-12-21 13:14:26.000000000 +0100
+++ nmap-3.78mm/scan_engine.cc	2004-12-21 13:23:28.000000000 +0100
@@ -1475,8 +1475,6 @@ static void ultrascan_port_update(UltraS
 
   probe = *probeI;
 
-  if (rcvdtime) ultrascan_adjust_times(USI, hss, probe, rcvdtime);
-
   if (probe->type == UltraProbe::UP_IP) {
     if (USI->prot_scan)
       proto = IPPROTO_IP;
@@ -1569,21 +1567,28 @@ static void ultrascan_port_update(UltraS
     }
   }
 
-  /* The rcvdtime check is because this func is called that way when
-     we give up on a probe because of too many retransmissions. */
-  if (oldstate != newstate && probe->tryno > hss->max_successful_tryno
-      && rcvdtime) {
-    hss->max_successful_tryno = probe->tryno;
-    if (o.debugging)
-      log_write(LOG_STDOUT, "Increased max_successful_tryno for %s to %d (packet drop)\n", hss->target->targetipstr(), hss->max_successful_tryno);
-    if (hss->max_successful_tryno > ((o.timing_level >= 4)? 4 : 3)) {
-      unsigned int olddelay = hss->sdn.delayms;
-      hss->boostScanDelay();
-      if (o.verbose && hss->sdn.delayms != olddelay) 
-	log_write(LOG_STDOUT, "Increasing send delay for %s from %d to %d due to max_successful_tryno increase to %d\n", 
-		  hss->target->targetipstr(), olddelay, hss->sdn.delayms, 
-		  hss->max_successful_tryno);
-    }
+  /* Is rcvdtime interesting? ICMP destination unreachable could be rate-limited (RFC1812)
+   * and is uninteresting for some scantypes. Also, if we didn't get new information
+   * from the response, consider the rcvdtime uninteresting too */
+  if (rcvdtime && (noresp_open_scan || (newstate != PORT_FILTERED && newstate != oldstate))) {
+      /* The rcvdtime check is because this func is called that way when
+         we give up on a probe because of too many retransmissions. */
+      
+      ultrascan_adjust_times(USI, hss, probe, rcvdtime);
+      
+      if (probe->tryno > hss->max_successful_tryno) {
+        hss->max_successful_tryno = probe->tryno;
+        if (o.debugging)
+          log_write(LOG_STDOUT, "Increased max_successful_tryno for %s to %d (packet drop)\n", hss->target->targetipstr(), hss->max_successful_tryno);
+        if (hss->max_successful_tryno > ((o.timing_level >= 4)? 4 : 3)) {
+          unsigned int olddelay = hss->sdn.delayms;
+          hss->boostScanDelay();
+          if (o.verbose && hss->sdn.delayms != olddelay) 
+            log_write(LOG_STDOUT, "Increasing send delay for %s from %d to %d due to max_successful_tryno increase to %d\n", 
+                      hss->target->targetipstr(), olddelay, hss->sdn.delayms, 
+                      hss->max_successful_tryno);
+        }
+      }
   }
 
   if (remove_probe) {