--- filter.inc.bak	2018-06-06 11:38:15.442508000 +1000
+++ filter.inc		2018-06-07 10:56:17.873309000 +1000
@@ -218,14 +218,32 @@
 			}
 			$gwstatus =& $a_gateways[$gateway['monitor']];
 			if (strstr($gwstatus['status'], "down")) {
-				$any_gateway_down = true;
-				break;
+				if (!empty($gateway['interface']))
+					$gwiface = $gateway['interface'];
+				else
+					$gwiface = get_real_interface($gateway['friendlyiface']);
+
+			        log_error("Removing NAT states for interface {$gwiface}");
+			        $nat_states = exec_command("/sbin/pfctl -i {$gwiface} -ss");
+ 			        $cleared_states = array();
+			        foreach (explode("\n", $nat_states) as $nat_state) {
+ 			                if (preg_match_all('/([\d\.]+):[\d]+[\s-><)]+/i', $nat_state, $ipv4_matches, PREG_SET_ORDER) != 3)
+						continue;
+					
+					$natsrc = $ipv4_matches[1][1];
+					$dst = $ipv4_matches[2][1];
+
+					if (empty($natsrc) || empty($dst) || in_array("{$natsrc},{$dst}", $cleared_states))
+						continue;
+
+					$cleared_states[] = "{$natsrc},{$dst}";
+					pfSense_kill_states($natsrc, $dst);
+			        }
+			        log_error("Removing states for interface {$gwiface}");
+			        mwexec("/sbin/pfctl -i {$gwiface} -Fs", true);
 			}
 		}
 	}
-	if ($any_gateway_down == true) {
-		mwexec("/sbin/pfctl -Fs");
-	}
 }
 
 /* reload filter sync */