diff --git a/lib/file/file_storage.php b/lib/file/file_storage.php
index 177cee6b5fb..4c2b6285622 100644
--- a/lib/file/file_storage.php
+++ b/lib/file/file_storage.php
@@ -710,7 +710,7 @@ class file_storage {
                 break;
 
             case 'image/png':
-                $quality = int($quality);
+                $quality = (int)$quality;
                 imagepng($img, NULL, $quality, NULL);
                 break;