diff --git a/app/subnets/scan/subnet-scan-execute-update-snmp-arp.php b/app/subnets/scan/subnet-scan-execute-update-snmp-arp.php
index a22a8af17d09408ba69ca4c3af583bca33207bb0..6f9589290884b953b06d0dab49617375ccd14450 100644
--- a/app/subnets/scan/subnet-scan-execute-update-snmp-arp.php
+++ b/app/subnets/scan/subnet-scan-execute-update-snmp-arp.php
@@ -72,7 +72,7 @@ if (sizeof($all_subnet_hosts)>0) {
                            $result[$Subnets->transform_address($r['ip'], "decimal")]['code'] = 0;
                            $result[$Subnets->transform_address($r['ip'], "decimal")]['status'] = "Online";
                            // update alive time and mac address
-                           @$Scan->ping_update_lastseen($result[$Subnets->transform_address($r['ip'], "decimal")]['id'], $r['mac']);
+                           @$Scan->ping_update_lastseen($result[$Subnets->transform_address($r['ip'], "decimal")]['id'], null, $r['mac']);
                        }
                    }
                }
diff --git a/functions/classes/class.Scan.php b/functions/classes/class.Scan.php
index aecf02637ee050b5842f15e3a8341e4622dc8f67..0f1e92ddc34bbcaa843a6c8bbdeea44aaa84b171 100644
--- a/functions/classes/class.Scan.php
+++ b/functions/classes/class.Scan.php
@@ -587,11 +587,15 @@ class Scan extends Common_functions {
 	 * @param datetime $datetime
 	 * @return void
 	 */
-	public function ping_update_lastseen ($id, $mac = null, $datetime = null) {
+	public function ping_update_lastseen ($id, $datetime = null, $mac = null) {
     	# set datetime
     	$datetime = is_null($datetime) ? date("Y-m-d H:i:s") : $datetime;
 		# execute
-		try { $this->Database->updateObject("ipaddresses", array("id"=>$id, "mac"=>$mac, "lastSeen"=>$datetime), "id"); }
+		$update_ipaddress = array("id"=>$id, "lastSeen"=>$datetime);
+		if (!is_null($mac)) {
+			$update_ipaddress["mac"] = $mac;
+		}
+		try { $this->Database->updateObject("ipaddresses", $update_ipaddress, "id"); }
 		catch (Exception $e) {
 			!$this->debugging ? : $this->Result->show("danger", $e->getMessage(), false);
 			# log