diff --git a/lib/persistence.php b/lib/persistence.php
index 38b47a7..36b964b 100644
--- a/lib/persistence.php
+++ b/lib/persistence.php
@@ -119,7 +119,7 @@ abstract class persistence
         if ($writtenBytes === false || $writtenBytes < strlen($data)) {
             throw new Exception('unable to write to file ' . $file, 13);
         }
-        chmod($file, 0640); // protect file access
+        @chmod($file, 0640); // protect file access
         return $file;
     }
 }