diff --git a/django/test/client.py b/django/test/client.py
index b1421901e27..47232ef1461 100644
--- a/django/test/client.py
+++ b/django/test/client.py
@@ -431,12 +431,14 @@ class Client(object):
 
     def logout(self):
         """
-        Removes the authenticated user's cookies.
+        Removes the authenticated user's cookies and session object.
 
         Causes the authenticated user to be logged out.
         """
         session = import_module(settings.SESSION_ENGINE).SessionStore()
-        session.delete(session_key=self.cookies[settings.SESSION_COOKIE_NAME].value)
+        session_cookie = self.cookies.get(settings.SESSION_COOKIE_NAME)
+        if session_cookie:
+            session.delete(session_key=session_cookie.value)
         self.cookies = SimpleCookie()
 
     def _handle_redirects(self, response):
diff --git a/tests/modeltests/test_client/models.py b/tests/modeltests/test_client/models.py
index dfc84169f39..c8f1d427259 100644
--- a/tests/modeltests/test_client/models.py
+++ b/tests/modeltests/test_client/models.py
@@ -423,4 +423,3 @@ class ClientTest(TestCase):
         self.assertEqual(mail.outbox[1].from_email, 'from@example.com')
         self.assertEqual(mail.outbox[1].to[0], 'second@example.com')
         self.assertEqual(mail.outbox[1].to[1], 'third@example.com')
-
diff --git a/tests/regressiontests/test_client_regress/models.py b/tests/regressiontests/test_client_regress/models.py
index 5d650923a4a..71d6a149d08 100644
--- a/tests/regressiontests/test_client_regress/models.py
+++ b/tests/regressiontests/test_client_regress/models.py
@@ -505,6 +505,14 @@ class SessionTests(TestCase):
         self.assertEqual(response.status_code, 200)
         self.assertEqual(response.content, 'YES')
 
+    def test_logout(self):
+        """Logout should work whether the user is logged in or not (#9978)."""
+        self.client.logout()
+        login = self.client.login(username='testclient',password='password')
+        self.failUnless(login, 'Could not log in')
+        self.client.logout()
+        self.client.logout()
+
 class RequestMethodTests(TestCase):
     def test_get(self):
         "Request a view via request method GET"