diff --git a/django/contrib/sessions/middleware.py b/django/contrib/sessions/middleware.py
index 434997d6164..82b217f8295 100644
--- a/django/contrib/sessions/middleware.py
+++ b/django/contrib/sessions/middleware.py
@@ -37,6 +37,7 @@ class SessionWrapper(object):
         return self._session.get(key, default)
 
     def pop(self, key, *args):
+        self.modified = self.modified or key in self._session 
         return self._session.pop(key, *args)
 
     def set_test_cookie(self):
diff --git a/django/contrib/sessions/tests.py b/django/contrib/sessions/tests.py
index 5a28effa869..e83442123ea 100644
--- a/django/contrib/sessions/tests.py
+++ b/django/contrib/sessions/tests.py
@@ -5,8 +5,24 @@ Inject data into the session cache.
 >>> s._session_cache = {}
 >>> s._session_cache['some key'] = 'exists'
 
+>>> s.accessed
+False
+>>> s.modified
+False
+
+>>> s.pop('non existant key', 'does not exist')
+'does not exist'
+>>> s.accessed
+True
+>>> s.modified
+False
+
 >>> s.pop('some key')
 'exists'
+>>> s.accessed
+True
+>>> s.modified
+True
 
 >>> s.pop('some key', 'does not exist')
 'does not exist'