diff --git a/django/middleware/locale.py b/django/middleware/locale.py
index 0867e3d60f..996b2d4c5b 100644
--- a/django/middleware/locale.py
+++ b/django/middleware/locale.py
@@ -1,7 +1,7 @@
 "This is the locale selecting middleware that will look at accept headers"
 
 from django.conf import settings
-from django.core.urlresolvers import (is_valid_path, get_resolver,
+from django.core.urlresolvers import (is_valid_path, get_resolver, get_script_prefix,
                                       LocaleRegexURLResolver)
 from django.http import HttpResponseRedirect
 from django.utils.cache import patch_vary_headers
@@ -45,9 +45,18 @@ class LocaleMiddleware(object):
                 path_valid = is_valid_path("%s/" % language_path, urlconf)
 
             if path_valid:
-                language_url = "%s://%s/%s%s" % (
-                    request.scheme, request.get_host(), language,
-                    request.get_full_path())
+                script_prefix = get_script_prefix()
+                language_url = "%s://%s%s" % (
+                    request.scheme,
+                    request.get_host(),
+                    # insert language after the script prefix and before the
+                    # rest of the URL
+                    request.get_full_path().replace(
+                        script_prefix,
+                        '%s%s/' % (script_prefix, language),
+                        1
+                    )
+                )
                 return self.response_redirect_class(language_url)
 
         if not (self.is_language_prefix_patterns_used()
diff --git a/tests/i18n/patterns/tests.py b/tests/i18n/patterns/tests.py
index 93284578b0..a4049fca13 100644
--- a/tests/i18n/patterns/tests.py
+++ b/tests/i18n/patterns/tests.py
@@ -3,7 +3,7 @@ from __future__ import unicode_literals
 import os
 
 from django.core.exceptions import ImproperlyConfigured
-from django.core.urlresolvers import reverse, clear_url_caches
+from django.core.urlresolvers import reverse, clear_url_caches, set_script_prefix
 from django.http import HttpResponsePermanentRedirect
 from django.middleware.locale import LocaleMiddleware
 from django.test import TestCase, override_settings
@@ -290,6 +290,25 @@ class URLResponseTests(URLTestCaseBase):
         self.assertEqual(response.context['LANGUAGE_CODE'], 'pt-br')
 
 
+class URLRedirectWithScriptAliasTests(URLTestCaseBase):
+    """
+    #21579 - LocaleMiddleware should respect the script prefix.
+    """
+    def setUp(self):
+        super(URLRedirectWithScriptAliasTests, self).setUp()
+        self.script_prefix = '/script_prefix'
+        set_script_prefix(self.script_prefix)
+
+    def tearDown(self):
+        super(URLRedirectWithScriptAliasTests, self).tearDown()
+        # reset script prefix
+        set_script_prefix('')
+
+    def test_language_prefix_with_script_prefix(self):
+        response = self.client.get('/prefixed/', HTTP_ACCEPT_LANGUAGE='en', SCRIPT_NAME=self.script_prefix)
+        self.assertRedirects(response, '%s/en/prefixed/' % self.script_prefix, target_status_code=404)
+
+
 class URLTagTests(URLTestCaseBase):
     """
     Test if the language tag works.