diff --git a/core/isbn.py b/core/isbn.py
index 4231087d..152ce452 100644
--- a/core/isbn.py
+++ b/core/isbn.py
@@ -111,9 +111,9 @@ class ISBN(object):
             else:
                 return self.__isbn13
     def __unicode__(self):
-        return unicode(self.to_string(type='13',hyphenate=False))
+        return unicode(self.to_string(type=self.type,hyphenate=False))
     def __str__(self):
-        return self.to_string(type='13',hyphenate=False)
+        return self.to_string(type=self.type,hyphenate=False)
     def __eq__(self, other):
         """ both equal if both valid checksums and ISBN 13 equal """
         if isinstance(other, ISBN):
diff --git a/core/tests.py b/core/tests.py
index db3db987..6c446aa5 100755
--- a/core/tests.py
+++ b/core/tests.py
@@ -347,7 +347,7 @@ class ISBNTest(TestCase):
         self.assertEqual(isbn.ISBN(python_10).to_string(10,True), '0-672-32978-6')
         
         # check casting to string -- ISBN 13
-        self.assertEqual(str(isbn.ISBN(python_10)), '9780672329784')
+        self.assertEqual(str(isbn.ISBN(python_10)), '0672329786')
         
         # test __eq__ and __ne__ and validate
         self.assertTrue(isbn.ISBN(milosz_10) == isbn.ISBN(milosz_13))
@@ -360,7 +360,8 @@ class ISBNTest(TestCase):
         
         # curious about set membership
         self.assertEqual(len(set([isbn.ISBN(milosz_10), isbn.ISBN(milosz_13)])),2)
-        self.assertEqual(len(set([str(isbn.ISBN(milosz_10)), str(isbn.ISBN(milosz_13))])),1)
+        self.assertEqual(len(set([str(isbn.ISBN(milosz_10)), str(isbn.ISBN(milosz_13))])),2)
+        self.assertEqual(len(set([isbn.ISBN(milosz_10).to_string(), isbn.ISBN(milosz_13).to_string()])),1)
 
 def suite():