diff --git a/src/etc/inc/interfaces.inc b/src/etc/inc/interfaces.inc
index 9560cee88..12e5f5ab5 100644
--- a/src/etc/inc/interfaces.inc
+++ b/src/etc/inc/interfaces.inc
@@ -2740,7 +2740,7 @@ function interface_6rd_configure($interface = 'wan', $wancfg)
     legacy_interface_create('stf', $stfiface);
     legacy_interface_flags($stfiface, 'link2');
 
-    mwexecf('/sbin/ifconfig %s inet6 %s/%s', array($stfiface, $rd6prefix, $rd6prefixlen));
+    mwexecf('/sbin/ifconfig %s inet6 %s/%s', array($stfiface, $rd6prefix, $rd6prefixlen + $wancfg['prefix-6rd-v4plen']));
     mwexecf('/sbin/ifconfig %s stfv4br %s', array($stfiface, $wancfg['gateway-6rd']));
     mwexecf('/sbin/ifconfig %s stfv4net %s/%s', array($stfiface, $ip4address, $wancfg['prefix-6rd-v4plen']));