diff --git a/django/middleware/locale.py b/django/middleware/locale.py
index 65a3893e9a..5643e484c6 100644
--- a/django/middleware/locale.py
+++ b/django/middleware/locale.py
@@ -35,7 +35,10 @@ class LocaleMiddleware(MiddlewareMixin):
         urlconf = getattr(request, 'urlconf', settings.ROOT_URLCONF)
         i18n_patterns_used, prefixed_default_language = is_language_prefix_patterns_used(urlconf)
 
-        if response.status_code == 404 and not language_from_path and i18n_patterns_used:
+        if (response.status_code == 404 and not language_from_path and
+                i18n_patterns_used and prefixed_default_language):
+            # Maybe the language code is missing in the URL? Try adding the
+            # language prefix and redirecting to that URL.
             language_path = '/%s%s' % (language, request.path_info)
             path_valid = is_valid_path(language_path, urlconf)
             path_needs_slash = (
diff --git a/docs/releases/1.10.4.txt b/docs/releases/1.10.4.txt
index 0f1f70e95d..86ce644fdf 100644
--- a/docs/releases/1.10.4.txt
+++ b/docs/releases/1.10.4.txt
@@ -23,3 +23,6 @@ Bugfixes
 * Fixed a ``QuerySet.update()`` crash on SQLite when updating a
   ``DateTimeField`` with an ``F()`` expression and a ``timedelta``
   (:ticket:`27544`).
+
+* Prevented ``LocaleMiddleware`` from redirecting on URLs that should return
+  404 when using ``prefix_default_language=False`` (:ticket:`27402`).
diff --git a/tests/i18n/tests.py b/tests/i18n/tests.py
index 38d99fa847..8d8d4c752e 100644
--- a/tests/i18n/tests.py
+++ b/tests/i18n/tests.py
@@ -1860,6 +1860,20 @@ class UnprefixedDefaultLanguageTests(SimpleTestCase):
         response = self.client.get('/de-simple-page/')
         self.assertEqual(response.content, b'Yes')
 
+    def test_no_redirect_on_404(self):
+        """
+        A request for a nonexistent URL shouldn't cause a redirect to
+        /<defaut_language>/<request_url> when prefix_default_language=False and
+        /<default_language>/<request_url> has a URL match (#27402).
+        """
+        # A match for /group1/group2/ must exist for this to act as a
+        # regression test.
+        response = self.client.get('/group1/group2/')
+        self.assertEqual(response.status_code, 200)
+
+        response = self.client.get('/nonexistent/')
+        self.assertEqual(response.status_code, 404)
+
 
 @override_settings(
     USE_I18N=True,
diff --git a/tests/i18n/urls_default_unprefixed.py b/tests/i18n/urls_default_unprefixed.py
index 92ef8c6246..85f9bf049b 100644
--- a/tests/i18n/urls_default_unprefixed.py
+++ b/tests/i18n/urls_default_unprefixed.py
@@ -6,5 +6,6 @@ from django.utils.translation import ugettext_lazy as _
 urlpatterns = i18n_patterns(
     url(r'^(?P<arg>[\w-]+)-page', lambda request, **arg: HttpResponse(_("Yes"))),
     url(r'^simple/$', lambda r: HttpResponse(_("Yes"))),
+    url(r'^(.+)/(.+)/$', lambda *args: HttpResponse()),
     prefix_default_language=False,
 )