diff --git a/phpBB/includes/acp/acp_styles.php b/phpBB/includes/acp/acp_styles.php
index af3fd7937c..6bd27a8bca 100644
--- a/phpBB/includes/acp/acp_styles.php
+++ b/phpBB/includes/acp/acp_styles.php
@@ -29,14 +29,31 @@ class acp_styles
 	protected $styles_path;
 	protected $styles_path_absolute = 'styles';
 	protected $default_style = 0;
+	protected $styles_list_cols = 0;
+	protected $reserved_style_names = array('adm', 'admin', 'all');
 
+	/** @var \phpbb\db\driver\driver_interface */
 	protected $db;
+
+	/** @var \phpbb\user */
 	protected $user;
+
+	/** @var \phpbb\template\template */
 	protected $template;
+
+	/** @var \phpbb\request\request_interface */
 	protected $request;
+
+	/** @var \phpbb\cache\driver\driver_interface */
 	protected $cache;
+
+	/** @var \phpbb\auth\auth */
 	protected $auth;
+
+	/** @var string */
 	protected $phpbb_root_path;
+
+	/** @var string */
 	protected $php_ext;
 
 	public function main($id, $mode)
@@ -164,6 +181,12 @@ class acp_styles
 		$last_installed = false;
 		foreach ($dirs as $dir)
 		{
+			if (in_array($dir, $this->reserved_style_names))
+			{
+				$messages[] = $this->user->lang('STYLE_NAME_RESERVED', htmlspecialchars($dir));
+				continue;
+			}
+
 			$found = false;
 			foreach ($styles as &$style)
 			{
@@ -809,7 +832,7 @@ class acp_styles
 	* Update styles tree
 	*
 	* @param array $styles Styles list, passed as reference
-	* @param array $style Current style, false if root
+	* @param array|false $style Current style, false if root
 	* @return bool True if something was updated, false if not
 	*/
 	protected function update_styles_tree(&$styles, $style = false)
@@ -1091,7 +1114,7 @@ class acp_styles
 	/**
 	* Install style
 	*
-	* @param $style style data
+	* @param array $style style data
 	* @return int Style id
 	*/
 	protected function install_style($style)
diff --git a/phpBB/language/en/acp/styles.php b/phpBB/language/en/acp/styles.php
index 506d569d56..e6b05c8282 100644
--- a/phpBB/language/en/acp/styles.php
+++ b/phpBB/language/en/acp/styles.php
@@ -74,6 +74,7 @@ $lang = array_merge($lang, array(
 	'STYLE_INSTALLED_RETURN_INSTALLED_STYLES'	=> 'Return to installed styles list',
 	'STYLE_INSTALLED_RETURN_UNINSTALLED_STYLES'	=> 'Install more styles',
 	'STYLE_NAME'				=> 'Style name',
+	'STYLE_NAME_RESERVED'		=> 'Style "%s" can not be installed, because the name is reserved.',
 	'STYLE_NOT_INSTALLED'		=> 'Style "%s" was not installed.',
 	'STYLE_PATH'				=> 'Style path',
 	'STYLE_UNINSTALL'			=> 'Uninstall',