--- ctools.module
+++ ctools.module
@@ -107,8 +107,11 @@
  */
 function ctools_include($file, $module = 'ctools', $dir = 'includes') {
   static $used = array();
+
+  $dir = '/' . $dir;
+
   if (!isset($used[$module][$dir][$file])) {
-    require_once './' . drupal_get_path('module', $module) . "/$dir/$file.inc";
+    require_once './' . drupal_get_path('module', $module) . "$dir/$file.inc";
     $used[$module][$dir][$file] = true;
   }
 }