Index: django/core/handlers/base.py
===================================================================
--- django/core/handlers/base.py	(revision 10031)
+++ django/core/handlers/base.py	(working copy)
@@ -24,7 +24,10 @@
         """
         from django.conf import settings
         from django.core import exceptions
-        self._request_middleware = []
+
+        # also serves as initialization guard
+        _request_middleware = []
+
         self._view_middleware = []
         self._response_middleware = []
         self._exception_middleware = []
@@ -49,7 +52,7 @@
                 continue
 
             if hasattr(mw_instance, 'process_request'):
-                self._request_middleware.append(mw_instance.process_request)
+                _request_middleware.append(mw_instance.process_request)
             if hasattr(mw_instance, 'process_view'):
                 self._view_middleware.append(mw_instance.process_view)
             if hasattr(mw_instance, 'process_response'):
@@ -57,6 +60,8 @@
             if hasattr(mw_instance, 'process_exception'):
                 self._exception_middleware.insert(0, mw_instance.process_exception)
 
+        self._request_middleware = _request_middleware
+
     def get_response(self, request):
         "Returns an HttpResponse object for the given HttpRequest"
         from django.core import exceptions, urlresolvers