diff --git a/actions/admin/settings/160.nameserver.php b/actions/admin/settings/160.nameserver.php
index 3574e4d9..e738c3f3 100644
--- a/actions/admin/settings/160.nameserver.php
+++ b/actions/admin/settings/160.nameserver.php
@@ -73,7 +73,7 @@ return array(
 					'settinggroup' => 'system',
 					'varname' => 'axfrservers',
 					'type' => 'string',
-					'string_type' => 'validate_ip',
+					'string_type' => 'validate_ip_incl_private',
 					'string_delimiter' => ',',
 					'string_emptyallowed' => true,
 					'default' => '',
diff --git a/lib/functions/formfields/string/function.validateFormFieldString.php b/lib/functions/formfields/string/function.validateFormFieldString.php
index 10ccca8f..addfc8b6 100644
--- a/lib/functions/formfields/string/function.validateFormFieldString.php
+++ b/lib/functions/formfields/string/function.validateFormFieldString.php
@@ -116,6 +116,17 @@ function validateFormFieldString($fieldname, $fielddata, $newfieldvalue)
 		        $returnvalue = ($newfieldvalue !== false ? true : 'invalidip');
 		    }
 		}
+                elseif (isset($fielddata['string_type']) && $fielddata['string_type'] == 'validate_ip_incl_private') {
+                    // check for empty value (it might be allowed)
+                    if (trim($newfieldvalue) == '') {
+                        $newfieldvalue = '';
+                        $returnvalue = 'stringmustntbeempty';
+                    } else {
+                        $newfieldvalue = validate_ip2($newfieldvalue, true, true, true);
+                        $returnvalue = ($newfieldvalue !== false ? true : 'invalidip');
+                    }
+                }
+
 		elseif (preg_match('/^[^\r\n\t\f\0]*$/D', $newfieldvalue)) {
 			$returnvalue = true;
 		}