diff --git a/scrapy/trunk/scrapy/http/headers.py b/scrapy/trunk/scrapy/http/headers.py
index a3344e29f..010db4bae 100644
--- a/scrapy/trunk/scrapy/http/headers.py
+++ b/scrapy/trunk/scrapy/http/headers.py
@@ -51,7 +51,9 @@ class Headers(CaselessDict):
         self.setdefault(key, default_list)
 
     def appendlist(self, key, value):
-        self.getlist(key).extend(self.normvalue(value))
+        lst = self.getlist(key)
+        lst.extend(self.normvalue(value))
+        self[key] = lst
 
     def items(self):
         return list(self.iteritems())
diff --git a/scrapy/trunk/scrapy/tests/test_http_headers.py b/scrapy/trunk/scrapy/tests/test_http_headers.py
index 3dc9f6670..f5810d6a7 100644
--- a/scrapy/trunk/scrapy/tests/test_http_headers.py
+++ b/scrapy/trunk/scrapy/tests/test_http_headers.py
@@ -87,6 +87,11 @@ class HeadersTest(unittest.TestCase):
         h1.appendlist('header1', 'value3')
         self.assertEqual(h1.getlist('header1'), ['value1', 'value3'])
 
+        h1 = Headers()
+        h1.appendlist('header1', 'value1')
+        h1.appendlist('header1', 'value3')
+        self.assertEqual(h1.getlist('header1'), ['value1', 'value3'])
+
     def test_setlist(self):
         h1 = Headers({'header1': 'value1'})
         self.assertEqual(h1.getlist('header1'), ['value1'])