diff --git a/lib/address.js b/lib/address.js
index 96d1a062a..b773f9d96 100644
--- a/lib/address.js
+++ b/lib/address.js
@@ -213,8 +213,9 @@ Address._transformBuffer = function(buffer, network, type){
  * @private
  */
 Address._transformPublicKey = function(pubkey){
+  var PublicKey = require('./publickey');
   var info = {};
-  if (!pubkey.constructor || (pubkey.constructor.name && pubkey.constructor.name !== 'PublicKey')) {
+  if (!(pubkey instanceof PublicKey)) {
     throw new TypeError('Address must be an instance of PublicKey.');
   }
   info.hashBuffer = Hash.sha256ripemd160(pubkey.toBuffer());
@@ -230,8 +231,9 @@ Address._transformPublicKey = function(pubkey){
  * @private
  */
 Address._transformScript = function(script, network){
+  var Script = require('./script');
   var info = {};
-  if (!script.constructor || (script.constructor.name && script.constructor.name !== 'Script')) {
+  if (!(script instanceof Script)) {
     throw new TypeError('Address must be an instance of Script.');
   }
   if (script.isScriptHashOut()) {