diff --git a/src/www/services_dhcpv6.php b/src/www/services_dhcpv6.php
index 610b277cb..a3b8dd6c9 100644
--- a/src/www/services_dhcpv6.php
+++ b/src/www/services_dhcpv6.php
@@ -153,7 +153,7 @@ if ($_SERVER['REQUEST_METHOD'] === 'GET') {
         if (!empty($pconfig['ddnsdomain']) && !is_domain($pconfig['ddnsdomain'])) {
             $input_errors[] = gettext("A valid domain name must be specified for the dynamic DNS registration.");
         }
-        if (!empty($pconfig['ddnsdomain']) && !is_ipaddrv4($pconfig['ddnsdomainprimary'])) {
+        if (!empty($pconfig['ddnsdomainprimary']) && !is_ipaddrv6($pconfig['ddnsdomainprimary'])) {
             $input_errors[] = gettext("A valid primary domain name server IPv6 address must be specified for the dynamic domain name.");
         }
         if (!empty($pconfig['ddnsdomainkey']) && base64_encode(base64_decode($pconfig['ddnsdomainkey'], true)) !== $pconfig['ddnsdomainkey']) {