diff --git a/docs/news.rst b/docs/news.rst
index 04cfa6e8b..2ec7ea293 100644
--- a/docs/news.rst
+++ b/docs/news.rst
@@ -3,6 +3,12 @@
 Release notes
 =============
 
+0.20 (not released yet)
+-----------------------
+
+- Request/Response url/body attributes are now immutable (modifying them had
+  been deprecated for a long time)
+
 0.18.0 (released 2013-08-09)
 ----------------------------
 
diff --git a/scrapy/http/common.py b/scrapy/http/common.py
index 34d5389bf..ba6ab277c 100644
--- a/scrapy/http/common.py
+++ b/scrapy/http/common.py
@@ -1,10 +1,6 @@
-import warnings
-from scrapy.exceptions import ScrapyDeprecationWarning
-
-def deprecated_setter(setter, attrname):
+def obsolete_setter(setter, attrname):
     def newsetter(self, value):
         c = self.__class__.__name__
-        warnings.warn("Don't modify %s.%s attribute, use %s.replace() instead" % \
-            (c, attrname, c), ScrapyDeprecationWarning, stacklevel=2)
-        return setter(self, value)
+        msg = "%s.%s is not modifiable, use %s.replace() instead" % (c, attrname, c)
+        raise AttributeError(msg)
     return newsetter
diff --git a/scrapy/http/request/__init__.py b/scrapy/http/request/__init__.py
index 1b14e2068..609a0d433 100644
--- a/scrapy/http/request/__init__.py
+++ b/scrapy/http/request/__init__.py
@@ -13,7 +13,7 @@ from scrapy.http.headers import Headers
 from scrapy.utils.trackref import object_ref
 from scrapy.utils.decorator import deprecated
 from scrapy.utils.url import escape_ajax
-from scrapy.http.common import deprecated_setter
+from scrapy.http.common import obsolete_setter
 
 class Request(object_ref):
 
@@ -60,7 +60,7 @@ class Request(object_ref):
         if ':' not in self._url:
             raise ValueError('Missing scheme in request url: %s' % self._url)
 
-    url = property(_get_url, deprecated_setter(_set_url, 'url'))
+    url = property(_get_url, obsolete_setter(_set_url, 'url'))
 
     def _get_body(self):
         return self._body
@@ -78,7 +78,7 @@ class Request(object_ref):
         else:
             raise TypeError("Request body must either str or unicode. Got: '%s'" % type(body).__name__)
 
-    body = property(_get_body, deprecated_setter(_set_body, 'body'))
+    body = property(_get_body, obsolete_setter(_set_body, 'body'))
 
     @property
     def encoding(self):
diff --git a/scrapy/http/response/__init__.py b/scrapy/http/response/__init__.py
index 46be1e362..7ff683eb6 100644
--- a/scrapy/http/response/__init__.py
+++ b/scrapy/http/response/__init__.py
@@ -9,7 +9,7 @@ import copy
 
 from scrapy.http.headers import Headers
 from scrapy.utils.trackref import object_ref
-from scrapy.http.common import deprecated_setter
+from scrapy.http.common import obsolete_setter
 
 class Response(object_ref):
 
@@ -39,7 +39,7 @@ class Response(object_ref):
             raise TypeError('%s url must be str, got %s:' % (type(self).__name__, \
                 type(url).__name__))
 
-    url = property(_get_url, deprecated_setter(_set_url, 'url'))
+    url = property(_get_url, obsolete_setter(_set_url, 'url'))
 
     def _get_body(self):
         return self._body
@@ -56,7 +56,7 @@ class Response(object_ref):
             raise TypeError("Response body must either str or unicode. Got: '%s'" \
                 % type(body).__name__)
 
-    body = property(_get_body, deprecated_setter(_set_body, 'body'))
+    body = property(_get_body, obsolete_setter(_set_body, 'body'))
 
     def __str__(self):
         return "<%d %s>" % (self.status, self.url)
diff --git a/scrapy/tests/test_http_request.py b/scrapy/tests/test_http_request.py
index 9d2f235cc..d3378148d 100644
--- a/scrapy/tests/test_http_request.py
+++ b/scrapy/tests/test_http_request.py
@@ -175,6 +175,11 @@ class RequestTest(unittest.TestCase):
         r = self.request_class("http://www.example.com", method=u"POST")
         assert isinstance(r.method, str)
 
+    def test_immutable_attributes(self):
+        r = self.request_class("http://example.com")
+        self.assertRaises(AttributeError, setattr, r, 'url', 'http://example2.com')
+        self.assertRaises(AttributeError, setattr, r, 'body', 'xxx')
+
 
 class FormRequestTest(RequestTest):
 
diff --git a/scrapy/tests/test_http_response.py b/scrapy/tests/test_http_response.py
index 26c66453a..0809340a1 100644
--- a/scrapy/tests/test_http_response.py
+++ b/scrapy/tests/test_http_response.py
@@ -107,6 +107,11 @@ class BaseResponseTest(unittest.TestCase):
     def _assert_response_encoding(self, response, encoding):
         self.assertEqual(response.encoding, resolve_encoding(encoding))
 
+    def test_immutable_attributes(self):
+        r = self.response_class("http://example.com")
+        self.assertRaises(AttributeError, setattr, r, 'url', 'http://example2.com')
+        self.assertRaises(AttributeError, setattr, r, 'body', 'xxx')
+
 class ResponseText(BaseResponseTest):
 
     def test_no_unicode_url(self):