diff --git a/django/test/client.py b/django/test/client.py
index b4bdde6931c..6ea811940d5 100644
--- a/django/test/client.py
+++ b/django/test/client.py
@@ -595,6 +595,7 @@ class Client(RequestFactory):
         else:
             request.session = engine.SessionStore()
         logout(request)
+        self.cookies = SimpleCookie()
 
     def _handle_redirects(self, response, **extra):
         "Follows any redirects by requesting responses from the server using GET."
diff --git a/docs/releases/1.6.1.txt b/docs/releases/1.6.1.txt
index 156378f928b..91c6a9e261c 100644
--- a/docs/releases/1.6.1.txt
+++ b/docs/releases/1.6.1.txt
@@ -37,3 +37,5 @@ Bug fixes
   multiple times (#21488, #17181).
 * Fixed a regression that unnecessarily triggered settings configuration when
   importing ``get_wsgi_application`` (#21486).
+* Fixed test client ``logout()`` method when using the cookie-based session
+  backend (#21448).
diff --git a/tests/test_client/tests.py b/tests/test_client/tests.py
index 0f3cba7e88d..ccd3b56d2e6 100644
--- a/tests/test_client/tests.py
+++ b/tests/test_client/tests.py
@@ -356,6 +356,10 @@ class ClientTest(TestCase):
         response = self.client.get('/test_client/login_protected_view/')
         self.assertRedirects(response, 'http://testserver/accounts/login/?next=/test_client/login_protected_view/')
 
+    @override_settings(SESSION_ENGINE="django.contrib.sessions.backends.signed_cookies")
+    def test_logout_cookie_sessions(self):
+        self.test_logout()
+
     def test_view_with_permissions(self):
         "Request a page that is protected with @permission_required"