diff --git a/scrapy/trunk/scrapy/contrib_exp/newitem/models.py b/scrapy/trunk/scrapy/contrib_exp/newitem/models.py
index 045a5aede..9f75846d9 100644
--- a/scrapy/trunk/scrapy/contrib_exp/newitem/models.py
+++ b/scrapy/trunk/scrapy/contrib_exp/newitem/models.py
@@ -11,14 +11,16 @@ class Item(object):
         self._fields = self._get_fields()
 
     def _get_fields(self):
-        return dict(i for i in self.__class__.__dict__.iteritems() if
-                    isinstance(i[1], ItemField))
+        return dict(i for i in self.__class__.__dict__.iteritems() \
+                    if isinstance(i[1], ItemField))
 
     def __setattr__(self, name, value):
-        if not name.startswith('_') and name in self._fields.keys():
-            self._values[name] = self._fields[name].to_python(value)
+        if not name.startswith('_'):
+            if name in self._fields.keys():
+                self._values[name] = self._fields[name].to_python(value)
+            else:
+                raise AttributeError(name)
         else:
-            # for now setting values that are not fields is permitted
             object.__setattr__(self, name, value)
 
     def __getattribute__(self, name):
@@ -26,10 +28,7 @@ class Item(object):
             try:
                 return self._values[name]
             except KeyError:
-                # what to to in this case?
-                # maybe return a default value:
-                # return self._fields[name].default_value()
-                return None
+                return self._fields[name].default_value()
         else:
             return object.__getattribute__(self, name)