diff --git a/backup/util/xml/parser/progressive_parser.class.php b/backup/util/xml/parser/progressive_parser.class.php
index 91bc85fc4b2..8b6df4b5ee9 100644
--- a/backup/util/xml/parser/progressive_parser.class.php
+++ b/backup/util/xml/parser/progressive_parser.class.php
@@ -149,7 +149,15 @@ class progressive_parser {
      * handling parser paths, see MDL-24381
      */
     public static function dirname($path) {
-        return str_replace('\\', '/', dirname($path));
+        static $cache = array();
+
+        if (!isset($cache[$path])) {
+            if (count($cache) > 4096)
+                $cache = array();
+            $cache[$path] = str_replace('\\', '/', dirname($path));
+        }
+
+        return $cache[$path];
     }
 
 // Protected API starts here