diff --git a/Classes/Driver/StorageDriver.php b/Classes/Driver/StorageDriver.php
index e1702c8..058e731 100644
--- a/Classes/Driver/StorageDriver.php
+++ b/Classes/Driver/StorageDriver.php
@@ -275,7 +275,7 @@ public function folderExists($folderIdentifier)
      */
     public function isWithin($folderIdentifier, $identifier)
     {
-        return GeneralUtility::isFirstPartOfStr($identifier, $folderIdentifier);
+        return GeneralUtility::isFirstPartOfStr('/' . ltrim($identifier, '/'), $folderIdentifier);
     }
 
     /**