diff --git a/src/domutil.js b/src/domutil.js
index bbfe9e1..fd76c12 100644
--- a/src/domutil.js
+++ b/src/domutil.js
@@ -31,6 +31,9 @@ function isValidURL(url) {
     if (!['', '443', '80'].includes(url.port)) {
         return false;
     }
+    if (url.hostname === 'localhost') {
+        return false;
+    }
     const lastDot = url.hostname.lastIndexOf('.');
     if (lastDot < 1) {
         return false;
@@ -38,6 +41,12 @@ function isValidURL(url) {
     if (url.hostname.slice(lastDot) === '.local') {
         return false;
     }
+    if (url.hostname.slice(lastDot + 1).match(/^[\d]+$/)) { // there should be no tld with numbers, possible ipv4
+        return false;
+    }
+    if (url.hostname.includes(':')) { // possibly an ipv6 addr; certainly an invalid hostname
+        return false;
+    }
     return true;
 }