diff --git a/radius.py b/radius.py
index 20ac5a3..c1751d4 100755
--- a/radius.py
+++ b/radius.py
@@ -326,7 +326,8 @@ def __init__(self, initialdata={}):
     def __getkeys(self, value):
         """Return tuple of code, name for given code or name."""
         if isinstance(value, int):
-            return value, ATTRS[value]
+            return value, ATTRS.get(value, None)
+
         else:
             id = ATTR_NAMES[value.lower()]
             return id, ATTRS[id]
@@ -355,8 +356,13 @@ def __setitem__(self, key, value):
         """
         try:
             code, name = self.__getkeys(key)
+
         except KeyError:
-            raise ValueError('Invalid radius attribute: %s' % key)
+            raise ValueError('Unknown radius attribute: %s' % key)
+
+        if name is None:
+            LOGGER.warning('Unknown radius attribute code %s' % code)
+
         values = self.get(code, [])
         values.append(value)
         UserDict.__setitem__(self, code, values)
diff --git a/tests.py b/tests.py
index 717abfc..289e8f4 100644
--- a/tests.py
+++ b/tests.py
@@ -52,10 +52,10 @@ def test_set_get_item(self):
         """Test setting and getting items."""
         a = radius.Attributes()
 
-        # Cannot use invalid radius codes or names.
-        with self.assertRaises(ValueError):
-            a[128] = b'bar'
+        # Can use unknown radius codes.
+        a[128] = b'bar'
 
+        # Cannot use invalid radius names.
         with self.assertRaises(ValueError):
             a['foo'] = b'bar'
 
@@ -66,7 +66,8 @@ def test_set_get_item(self):
         self.assertEqual([b'foobar'], a[radius.ATTR_USER_NAME])
         self.assertEqual([b'foobar'], a['user-name'])
         self.assertEqual([b'foobar'], a['user-Name'])
-        self.assertEqual([('User-Name', ['foobar'])], list(a.nameditems()))
+        self.assertEqual(
+            [(None, ['bar']), ('User-Name', ['foobar'])], list(a.nameditems()))
 
     def test_init_update(self):
         """Test __init__ and update."""