diff --git a/CHANGELOG b/CHANGELOG
index 4ef827e4a..0979279bf 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,5 +1,8 @@
 #Nmap Changelog ($Id$); -*-text-*-
 
+o [GH#863] Avoid reporting negative latencies due to matching an ARP or ND
+  response to a probe sent after it was recieved. [Daniel Miller]
+
 o [ncat][GH#1441] To avoid confusion and to support default proxy ports,
   option --proxy now requires a literal IPv6 address to be specified using
   square-bracket notation, such as --proxy [2001:db8::123]:456. [nnposter] 
diff --git a/scan_engine_raw.cc b/scan_engine_raw.cc
index 3210d42af..8f1e90dca 100644
--- a/scan_engine_raw.cc
+++ b/scan_engine_raw.cc
@@ -1594,7 +1594,11 @@ bool get_arp_result(UltraScanInfo *USI, struct timeval *stime) {
         continue;
       }
       probeI = hss->probes_outstanding.end();
-      probeI--;
+      do {
+        /* Delay in libpcap could mean we sent another probe *after* this
+         * response was received. Search back for the last probe before rcvdtime. */
+        probeI--;
+      } while (TIMEVAL_AFTER((*probeI)->sent, rcvdtime) && probeI != hss->probes_outstanding.begin());
       ultrascan_host_probe_update(USI, hss, probeI, HOST_UP, &rcvdtime);
       /* Now that we know the host is up, we can forget our other probes. */
       hss->destroyAllOutstandingProbes();
@@ -1666,7 +1670,11 @@ bool get_ns_result(UltraScanInfo *USI, struct timeval *stime) {
         /* TODO: I suppose I should really mark the @@# host as up */
       }
       probeI = hss->probes_outstanding.end();
-      probeI--;
+      do {
+        /* Delay in libpcap could mean we sent another probe *after* this
+         * response was received. Search back for the last probe before rcvdtime. */
+        probeI--;
+      } while (TIMEVAL_AFTER((*probeI)->sent, rcvdtime) && probeI != hss->probes_outstanding.begin());
       ultrascan_host_probe_update(USI, hss, probeI, HOST_UP, &rcvdtime);
       /* Now that we know the host is up, we can forget our other probes. */
       hss->destroyAllOutstandingProbes();