diff --git a/src/Module/Install.php b/src/Module/Install.php
index d1e2677585..de19bc86ab 100644
--- a/src/Module/Install.php
+++ b/src/Module/Install.php
@@ -43,6 +43,10 @@ class Install extends BaseModule
 	{
 		$a = self::getApp();
 
+		if (!$a->getMode()->isInstall()) {
+			Core\System::httpExit(403);
+		}
+
 		// route: install/testrwrite
 		// $baseurl/install/testrwrite to test if rewrite in .htaccess is working
 		if ($a->getArgumentValue(1, '') == 'testrewrite') {