diff --git a/data/web/edit.php b/data/web/edit.php
index 13ceded5..31b46e9f 100644
--- a/data/web/edit.php
+++ b/data/web/edit.php
@@ -106,7 +106,7 @@ if (isset($_SESSION['mailcow_cc_role'])) {
         <div class="form-group">
           <label class="control-label col-sm-2" for="username_new"><?=$lang['edit']['username'];?></label>
           <div class="col-sm-10">
-            <input class="form-control" type="text" name="username_new" value="<?=htmlspecialchars($domain_admin);?>" />
+            <input class="form-control" type="text" name="username_new" value="<?=htmlspecialchars($domain_admin);?>" required onkeyup="this.value = this.value.toLowerCase();" />
           </div>
         </div>
         <div class="form-group">
@@ -197,14 +197,14 @@ if (isset($_SESSION['mailcow_cc_role'])) {
       $result = admin('details', $admin);
       if (!empty($result)) {
       ?>
-      <h4><?=$lang['edit']['domain_admin'];?></h4>
+      <h4><?=$lang['edit']['admin'];?></h4>
       <br>
       <form class="form-horizontal" data-id="editadmin" role="form" method="post" autocomplete="off">
         <input type="hidden" value="0" name="active">
         <div class="form-group">
           <label class="control-label col-sm-2" for="username_new"><?=$lang['edit']['username'];?></label>
           <div class="col-sm-10">
-            <input class="form-control" type="text" name="username_new" value="<?=htmlspecialchars($admin);?>" />
+            <input class="form-control" type="text" name="username_new" onkeyup="this.value = this.value.toLowerCase();" required value="<?=htmlspecialchars($admin);?>" />
           </div>
         </div>
         <div class="form-group">
diff --git a/data/web/lang/lang.de.json b/data/web/lang/lang.de.json
index 4c724bbb..3f8da317 100644
--- a/data/web/lang/lang.de.json
+++ b/data/web/lang/lang.de.json
@@ -504,6 +504,7 @@
     },
     "edit": {
         "active": "Aktiv",
+        "admin": "Administrator bearbeiten",
         "advanced_settings": "Erweiterte Einstellungen",
         "alias": "Alias bearbeiten",
         "allow_from_smtp": "Nur folgende IPs für <b>SMTP</b> erlauben",
diff --git a/data/web/lang/lang.en.json b/data/web/lang/lang.en.json
index 9364fa6c..7eafac82 100644
--- a/data/web/lang/lang.en.json
+++ b/data/web/lang/lang.en.json
@@ -502,6 +502,7 @@
     },
     "edit": {
         "active": "Active",
+        "admin": "Edit administrator",
         "advanced_settings": "Advanced settings",
         "alias": "Edit alias",
         "allow_from_smtp": "Only allow these IPs to use <b>SMTP</b>",