diff --git a/mmlc_installer.php b/mmlc_installer.php
index 34cb1c44..ee8cad68 100644
--- a/mmlc_installer.php
+++ b/mmlc_installer.php
@@ -46,6 +46,7 @@ public function invokeIndex()
     public function doSystemCheck()
     {
         $errors = [];
+
         if (!ini_get('allow_url_fopen')) {
             $errors[] = 'No connection to server. <strong>allow_url_fopen</strong> has to be activated in php.ini.';
         }
@@ -54,6 +55,10 @@ public function doSystemCheck()
             $errors[] = 'Current PHP version is ' . PHP_VERSION . '. The MMLC needs version <strong>' . self::REQUIRED_PHP_VERSION . '</strong> or higher.';
         }
 
+        if (!file_exists(__DIR__ . '/includes/classes/modified_api.php')) {
+            $errors[] = '<code style="display: inline; padding: 2px 4px;">' . __DIR__ . '</code> is the wrong installation directory. Please use the shop root.';
+        }
+
         return $errors;
     }