diff --git a/phpBB/phpbb/install/controller/install.php b/phpBB/phpbb/install/controller/install.php
index 469e2608a4..904f5920c2 100644
--- a/phpBB/phpbb/install/controller/install.php
+++ b/phpBB/phpbb/install/controller/install.php
@@ -111,7 +111,7 @@ class install
 	{
 		if ($this->install_helper->is_phpbb_installed())
 		{
-			throw new http_exception(404, 'PAGE_NOT_FOUND');
+			die ('phpBB is already installed');
 		}
 
 		$this->template->assign_vars(array(
diff --git a/phpBB/phpbb/install/helper/install_helper.php b/phpBB/phpbb/install/helper/install_helper.php
index c1506de5bf..ffe36cd645 100644
--- a/phpBB/phpbb/install/helper/install_helper.php
+++ b/phpBB/phpbb/install/helper/install_helper.php
@@ -47,14 +47,14 @@ class install_helper
 	 */
 	public function is_phpbb_installed()
 	{
-		$config_path = $this->phpbb_root_path . 'config' . $this->php_ext;
+		$config_path = $this->phpbb_root_path . 'config.' . $this->php_ext;
 		$install_lock_path = $this->phpbb_root_path . 'cache/install_lock';
 
-		if (file_exists($config_path) && !file_exists($install_lock_path))
+		if (file_exists($config_path) && !file_exists($install_lock_path) && filesize($config_path))
 		{
-			include_once $config_path;
+			return true;
 		}
 
-		return defined('PHPBB_INSTALLED');
+		return false;
 	}
 }