diff --git a/system/controllers/customers.php b/system/controllers/customers.php
index d5828183..b6222faa 100644
--- a/system/controllers/customers.php
+++ b/system/controllers/customers.php
@@ -540,6 +540,12 @@ switch ($action) {
         }
         if ($oldPppoeUsername != $pppoe_username) {
             $pppoeDiff = true;
+            if(ORM::for_table('tbl_customers')->where('pppoe_username', $pppoe_username)->find_one()){
+                $msg.= Lang::T('PPPoE Username already used by another customer') . '<br>';
+            }
+            if(ORM::for_table('tbl_customers')->where('username', $pppoe_username)->find_one()){
+                $msg.= Lang::T('PPPoE Username already used by another customer') . '<br>';
+            }
         }
         if ($password != '' && $oldPassPassword != $password) {
             $passDiff = true;