diff --git a/scrapy/trunk/scrapy/contrib_exp/newitem/models.py b/scrapy/trunk/scrapy/contrib_exp/newitem/models.py
index 0d38316b2..b102526aa 100644
--- a/scrapy/trunk/scrapy/contrib_exp/newitem/models.py
+++ b/scrapy/trunk/scrapy/contrib_exp/newitem/models.py
@@ -22,22 +22,25 @@ class Item(Declarative, ScrapedItem):
         return self.__class__.fields
 
     def __setattr__(self, name, value):
-        if not name.startswith('_'):
-            if name in self._fields.keys():
-                self._values[name] = self._fields[name].assign(value)
-            else:
-                raise AttributeError(name)
+        if name.startswith('_'):
+            return object.__setattr__(self, name, value)
+
+        if name in self._fields.keys():
+            self._values[name] = self._fields[name].assign(value)
         else:
-            object.__setattr__(self, name, value)
+            raise AttributeError(name)
 
     def __getattribute__(self, name):
-        if not name.startswith('_') and name in self._fields.keys():
+        if name.startswith('_'):
+            return object.__getattribute__(self, name)
+        
+        if name in self._fields.keys():
             try:
                 return self._values[name]
             except KeyError:
                 return self._fields[name].default
         else:
-            return object.__getattribute__(self, name)
+            raise AttributeError(name)
 
     def __repr__(self):
         """