diff --git a/info.textgrid.middleware.tgauth.webauth/tglib/RBAC.class.php b/info.textgrid.middleware.tgauth.webauth/tglib/RBAC.class.php
index 4d3ba554caa4b838b7371a82bfec749f5d649390..e1c6890fb2ab213dc8cfe6a64eee431de447c377 100644
--- a/info.textgrid.middleware.tgauth.webauth/tglib/RBAC.class.php
+++ b/info.textgrid.middleware.tgauth.webauth/tglib/RBAC.class.php
@@ -37,7 +37,7 @@ class RBAC {
     $xpath->registerNamespace("c", "http://textgrid.info/namespaces/middleware/tgwebauth");
 
     $this->rbacbase = $xpath->query("/c:conf/c:authz[@instance='${authZinstance}']/c:rbacbase")->item(0)->nodeValue;
-    if ($this->rbacbase->length == 0) {
+    if (!isset ($this->rbacbase) || strlen($this->rbacbase) == 0) {
 	echo "Error: '${authZinstance}' has no RBAC base configured!<br/>\n";
 	return null;
     }