diff --git a/lib/stripe.rb b/lib/stripe.rb
index 81458910..4033a5cd 100644
--- a/lib/stripe.rb
+++ b/lib/stripe.rb
@@ -260,7 +260,11 @@ module Stripe
       shortname = self.name.split('::')[-1]
       "/#{CGI.escape(shortname.downcase)}s"
     end
-    def url; "#{self.class.url}/#{CGI.escape(id)}"; end
+    def url
+      id = self['id']
+      raise InvalidRequestError.new("Could not determine which URL to request: #{self.class} instance has invalid ID: #{id.inspect}", 'id') unless id
+      "#{self.class.url}/#{CGI.escape(id)}"
+    end
 
     def refresh
       response, api_key = Stripe.request(:get, url, @api_key)
diff --git a/test/test_stripe.rb b/test/test_stripe.rb
index 2fd0f04a..d0546e4e 100644
--- a/test/test_stripe.rb
+++ b/test/test_stripe.rb
@@ -1,3 +1,4 @@
+# -*- coding: utf-8 -*-
 require File.dirname(__FILE__) + '/test_helper.rb'
 require 'test/unit'
 require 'context'
@@ -76,6 +77,11 @@ class TestStripeRuby < Test::Unit::TestCase
         assert_raises(Stripe::InvalidRequestError) { c.refresh }
       end
 
+      test "requesting with no ID shuold result in an InvalidRequestError with no request" do
+        c = Stripe::Customer.new
+        assert_raises(Stripe::InvalidRequestError) { c.refresh }
+      end
+
       test "loading an object should issue a GET request" do
         @mock.expects(:get).once.returns(test_response(test_customer))
         c = Stripe::Customer.new("test_customer")