diff --git a/packer/type.soa.js b/packer/type.soa.js
index eccb416..40c86d8 100644
--- a/packer/type.soa.js
+++ b/packer/type.soa.js
@@ -15,7 +15,7 @@
 
 exports.DNS_PACKER_TYPE_SOA = function (ab, dv, total, record) {
   function notNumber(n) {
-    return 'number' === typeof n && !isNaN(n);
+    return 'number' !== typeof n || isNaN(n);
   }
 
   if (!record.primary && !record.name_server) {