diff --git a/interface/web/sites/form/shell_user.tform.php b/interface/web/sites/form/shell_user.tform.php
index 062ed6e0b0712365687f7cfb7b9c443ac6385549..8ad815998caab3912ef446fdbb8b4457c093000c 100644
--- a/interface/web/sites/form/shell_user.tform.php
+++ b/interface/web/sites/form/shell_user.tform.php
@@ -93,6 +93,13 @@ $form["tabs"]['shell'] = array (
 				1 => array ( 'type' => 'REGEX',
 					'regex' => '/^[\w\.\-]{0,32}$/',
 					'errmsg'=> 'username_error_regex'),
+				2 => array(
+							'type' => 'CUSTOM',
+							'class' => 'validate_systemuser',
+							'function' => 'check_sysuser',
+							'check_names' => true,
+							'errmsg' => 'invalid_username_txt'
+						),
 			),
 			'default' => '',
 			'value'  => '',
diff --git a/interface/web/sites/form/web_domain.tform.php b/interface/web/sites/form/web_domain.tform.php
index 651b64355a77aa10b52bc373ff895b658fd0de71..04b0e1290a4acb87e6eea94cce04e79f0d2345b8 100644
--- a/interface/web/sites/form/web_domain.tform.php
+++ b/interface/web/sites/form/web_domain.tform.php
@@ -582,6 +582,13 @@ if($_SESSION["s"]["user"]["typ"] == 'admin') {
 				'formtype' => 'TEXT',
 				'validators' => array (  0 => array ( 'type' => 'NOTEMPTY',
 						'errmsg'=> 'sysuser_error_empty'),
+						1 => array(
+							'type' => 'CUSTOM',
+							'class' => 'validate_systemuser',
+							'function' => 'check_sysuser',
+							'check_names' => true,
+							'errmsg' => 'invalid_system_user_or_group_txt'
+						),
 				),
 				'default' => '',
 				'value'  => '',
@@ -593,6 +600,13 @@ if($_SESSION["s"]["user"]["typ"] == 'admin') {
 				'formtype' => 'TEXT',
 				'validators' => array (  0 => array ( 'type' => 'NOTEMPTY',
 						'errmsg'=> 'sysgroup_error_empty'),
+						1 => array(
+							'type' => 'CUSTOM',
+							'class' => 'validate_systemuser',
+							'function' => 'check_sysuser',
+							'check_names' => true,
+							'errmsg' => 'invalid_system_user_or_group_txt'
+						),
 				),
 				'default' => '',
 				'value'  => '',
diff --git a/interface/web/sites/lib/lang/en_shell_user.lng b/interface/web/sites/lib/lang/en_shell_user.lng
index 2ae9b4e6a1373c9dd7f3e932e0613d9a95cd58f0..c3f21d52d73152c68cb288d2d4b568bc7fe48540 100644
--- a/interface/web/sites/lib/lang/en_shell_user.lng
+++ b/interface/web/sites/lib/lang/en_shell_user.lng
@@ -31,4 +31,5 @@ $wb['username_not_allowed_txt'] = 'The username is not allowed.';
 $wb['invalid_system_user_or_group_txt'] = 'Invalid system user or group';
 $wb['directory_error_regex'] = 'Invalid directory';
 $wb['shell_error_regex'] = 'Invalid shell';
+$wb['invalid_username_txt'] = 'Invalid Username';
 ?>
diff --git a/interface/web/sites/lib/lang/en_web_domain.lng b/interface/web/sites/lib/lang/en_web_domain.lng
index 8c8f90eb0fd69b78b1b9546b55d8f13ca69693ec..0478e9972c4cbf0fae8dcf43660d40b4f155fdd4 100644
--- a/interface/web/sites/lib/lang/en_web_domain.lng
+++ b/interface/web/sites/lib/lang/en_web_domain.lng
@@ -127,4 +127,5 @@ $wb['backup_excludes_txt'] = 'Excluded Directories';
 $wb['backup_excludes_note_txt'] = '(Separate multiple directories with commas. Example: web/cache/*,web/backup)';
 $wb['backup_excludes_error_regex'] = 'The excluded directories contain invalid characters.';
 $wb['invalid_custom_php_ini_settings_txt'] = 'Invalid php.ini settings';
+$wb['invalid_system_user_or_group_txt'] = 'Invalid system user or group';
 ?>
\ No newline at end of file