diff --git a/scrapy/contrib/loader/__init__.py b/scrapy/contrib/loader/__init__.py
index 7be2524b9..c861f8a24 100644
--- a/scrapy/contrib/loader/__init__.py
+++ b/scrapy/contrib/loader/__init__.py
@@ -80,7 +80,7 @@ class ItemLoader(object):
 
     def load_item(self):
         item = self.item
-        for field_name in self._values:
+        for field_name in tuple(self._values):
             value = self.get_output_value(field_name)
             if value is not None:
                 item[field_name] = value
diff --git a/tests/test_contrib_loader.py b/tests/test_contrib_loader.py
index 6af4cf70c..fd65e8200 100644
--- a/tests/test_contrib_loader.py
+++ b/tests/test_contrib_loader.py
@@ -85,6 +85,27 @@ class BasicItemLoaderTest(unittest.TestCase):
         il.replace_value('sku', [valid_fragment], re=sku_re)
         self.assertEqual(il.load_item()['sku'], u'1234')
 
+    def test_self_referencing_loader(self):
+        class MyLoader(ItemLoader):
+            url_out = TakeFirst()
+
+            def img_url_out(self, values):
+                return (self.get_output_value('url') or '') + values[0]
+
+        il = MyLoader(item={})
+        il.add_value('url', 'http://example.com/')
+        il.add_value('img_url', '1234.png')
+        self.assertEqual(il.load_item(), {
+            'url': 'http://example.com/',
+            'img_url': 'http://example.com/1234.png',
+        })
+
+        il = MyLoader(item={})
+        il.add_value('img_url', '1234.png')
+        self.assertEqual(il.load_item(), {
+            'img_url': '1234.png',
+        })
+
     def test_add_value(self):
         il = TestItemLoader()
         il.add_value('name', u'marta')