diff --git a/django/contrib/auth/hashers.py b/django/contrib/auth/hashers.py
index c49c25ce66..a211f1e522 100644
--- a/django/contrib/auth/hashers.py
+++ b/django/contrib/auth/hashers.py
@@ -56,6 +56,8 @@ def check_password(password, encoded, setter=None, preferred='default'):
     hasher = identify_hasher(encoded)
 
     must_update = hasher.algorithm != preferred.algorithm
+    if not must_update:
+        must_update = hasher.must_update(encoded)
     is_correct = hasher.verify(password, encoded)
     if setter and is_correct and must_update:
         setter(password)
@@ -212,6 +214,9 @@ class BasePasswordHasher(object):
         """
         raise NotImplementedError('subclasses of BasePasswordHasher must provide a safe_summary() method')
 
+    def must_update(self, encoded):
+        return False
+
 
 class PBKDF2PasswordHasher(BasePasswordHasher):
     """
@@ -250,6 +255,10 @@ class PBKDF2PasswordHasher(BasePasswordHasher):
             (_('hash'), mask_hash(hash)),
         ])
 
+    def must_update(self, encoded):
+        algorithm, iterations, salt, hash = encoded.split('$', 3)
+        return int(iterations) != self.iterations
+
 
 class PBKDF2SHA1PasswordHasher(PBKDF2PasswordHasher):
     """
diff --git a/django/contrib/auth/tests/test_hashers.py b/django/contrib/auth/tests/test_hashers.py
index 627c56eb18..d0fc9895e9 100644
--- a/django/contrib/auth/tests/test_hashers.py
+++ b/django/contrib/auth/tests/test_hashers.py
@@ -245,6 +245,37 @@ class TestUtilsHashPass(unittest.TestCase):
             self.assertFalse(check_password('WRONG', encoded, setter))
             self.assertFalse(state['upgraded'])
 
+    def test_pbkdf2_upgrade(self):
+        self.assertEqual('pbkdf2_sha256', get_hasher('default').algorithm)
+        hasher = get_hasher('default')
+        self.assertNotEqual(hasher.iterations, 1)
+
+        old_iterations = hasher.iterations
+        try:
+            # Generate a password with 1 iteration.
+            hasher.iterations = 1
+            encoded = make_password('letmein')
+            algo, iterations, salt, hash = encoded.split('$', 3)
+            self.assertEqual(iterations, '1')
+
+            state = {'upgraded': False}
+            def setter(password):
+                state['upgraded'] = True
+
+            # Check that no upgrade is triggerd
+            self.assertTrue(check_password('letmein', encoded, setter))
+            self.assertFalse(state['upgraded'])
+
+            # Revert to the old iteration count and ...
+            hasher.iterations = old_iterations
+
+            # ... check if the password would get updated to the new iteration count.
+            self.assertTrue(check_password('letmein', encoded, setter))
+            self.assertTrue(state['upgraded'])
+        finally:
+            hasher.iterations = old_iterations
+
+
     def test_load_library_no_algorithm(self):
         with self.assertRaises(ValueError) as e:
             BasePasswordHasher()._load_library()