diff --git a/app/code/core/Mage/Adminhtml/Model/Config/Data.php b/app/code/core/Mage/Adminhtml/Model/Config/Data.php
index 749ee52..b164eb9 100644
--- a/app/code/core/Mage/Adminhtml/Model/Config/Data.php
+++ b/app/code/core/Mage/Adminhtml/Model/Config/Data.php
@@ -132,8 +132,10 @@ class Mage_Adminhtml_Model_Config_Data extends Varien_Object
                 /**
                  * Get field backend model
                  */
-                $backendClass = $fieldConfig->backend_model;
-                if (!$backendClass) {
+                if (isset($fieldConfig->backend_model)) {
+                    $backendClass = $fieldConfig->backend_model;
+                }
+                if (!isset($backendClass)) {
                     $backendClass = 'core/config_data';
                 }