diff --git a/src/etc/inc/util.inc b/src/etc/inc/util.inc
index 92183e79661..a38f4b73ff2 100644
--- a/src/etc/inc/util.inc
+++ b/src/etc/inc/util.inc
@@ -424,7 +424,12 @@ function calculate_ipv6_delegation_length($if)
             break;
         case 'dhcp6':
             $dhcp6cfg = $config['interfaces'][$if];
-            if (is_numeric($dhcp6cfg['dhcp6-ia-pd-len'])) {
+            $realif = get_real_interface($if);
+            if(file_exists("/tmp/{$realif}_pdinfo")){
+                $file_pdinfo = file_get_contents("/tmp/{$realif}_pdinfo");
+                $pdinfo = explode('/',$file_pdinfo);
+                $pdlen = $pdinfo[1];
+            } else if (is_numeric($dhcp6cfg['dhcp6-ia-pd-len'])) {
                 $pdlen = $dhcp6cfg['dhcp6-ia-pd-len'];
             }
             break;