diff --git a/workflow/engine/classes/class.pmScript.php b/workflow/engine/classes/class.pmScript.php
index d5cc60ef3..1da77dfad 100644
--- a/workflow/engine/classes/class.pmScript.php
+++ b/workflow/engine/classes/class.pmScript.php
@@ -52,7 +52,10 @@ function __autoload ($sClassName)
     }
 }
 
-Bootstrap::setConstantRelatedWs('SYS_SYS');
+if (defined( 'SYS_SYS' )) {
+    Bootstrap::setConstantsRelatedWs('SYS_SYS');
+}
+
 if (!defined('PATH_WORKSPACE')) {
     define('PATH_WORKSPACE', PATH_DATA_SITE);