diff --git a/lib/functions.php b/lib/functions.php
index cf988e5..931ad73 100644
--- a/lib/functions.php
+++ b/lib/functions.php
@@ -7,43 +7,44 @@ Copyright (C) 2011-2023 Thomas Hooge
 SPDX-License-Identifier: GPL-3.0-or-later
 *****************************************************************************/
 
-// strip mac address to 12 char string
-function strip_mac($mac) {
+function strip_mac($mac, $caps=true) {
+    // strip mac address to 12 char string
     // strip chars we don't need
-    $mac = preg_replace("|[^a-fA-F0-9]|", "", $mac);
-
-    // capitalize (just because it looks better eh)
-    $mac = strtoupper($mac);
-
-    // and return
-    return ($mac);
+    $mac = preg_replace('/[^a-fA-F0-9]/', '', $mac);
+    if ($caps) {
+        $mac = strtoupper($mac);
+    } else {
+        $mac = strtolower($mac);
+    }
+    return $mac;
 }
 
-// rebuild mac address
-function write_mac($mac) {
-    // check string length
-    if (strlen($mac)!=12) {
+function write_mac($mac, $user_mac='xx:xx:xx:xx:xx:xx') {
+    // rebuild mac address using user supplied format
+
+    if (strlen($mac) != 12) {
         // if the MAC is empty, or for whatever reason incorrect, just return
         return $mac;
-    } else {
-        // count to 12...
-        for ($i=0; $i<12; $i++) {
-            // ... and strip mac to pieces
-            ${"mac".$i} = $mac{$i};
-        }
-
-        // get user preference
-        $user_mac = $_SESSION['suser_mac'];
+    }
 
-        // count to 12 again...
-        for($i=0; $i<12; $i++) {
-            // ... and replace user preference with pieces
-            $user_mac = preg_replace("/x/", ${"mac".$i}, $user_mac, 1);
-        }
+    // check format of user mac: count upper or lower char
+    $chars = count_chars($user_mac, 1);
+    if (array_key_exists(88, $chars) and $chars[88] == 12) {
+        $pattern = '/X/';
+        $mac = strtoupper($mac);
+    } elseif (array_key_exists(120, $chars) and $chars[120] == 12) {
+        $pattern = '/x/';
+        $mac = strtolower($mac);
+    } else {
+        // invalid format
+        return $mac;
+    }
 
-        // and return
-        return $user_mac;
+    for($i=0; $i<12; $i++) {
+        $user_mac = preg_replace($pattern, $mac[$i], $user_mac, 1);
     }
+
+    return $user_mac;
 }
 
 // redirect page
diff --git a/node.php b/node.php
index 6e2b4ab..4ae4fee 100644
--- a/node.php
+++ b/node.php
@@ -231,7 +231,7 @@ $sth = $dbh->prepare($sql);
 $sth->execute([$id]);
 
 $node = $sth->fetch(PDO::FETCH_OBJ);
-$node->mac = write_mac($node->mac);
+$node->mac = write_mac($node->mac, $_SESSION['suser_mac']);
 $smarty->assign("node", $node);
 
 // nat
@@ -281,6 +281,7 @@ $sql = "SELECT node_id AS id, node_ip AS ip, node_mac AS mac,
 $sth = $dbh->prepare($sql);
 $sth->execute([$id]);
 $node = $sth->fetch(PDO::FETCH_OBJ);
+$node->mac = write_mac($node->mac, $_SESSION['suser_mac']);
 $node->flags = explode(',', $node->flags);
 $smarty->assign("node", $node);