diff --git a/django/utils/datastructures.py b/django/utils/datastructures.py
index 6c60675d38..76f7459032 100644
--- a/django/utils/datastructures.py
+++ b/django/utils/datastructures.py
@@ -37,6 +37,9 @@ class OrderedSet(object):
     def __nonzero__(self):      # Python 2 compatibility
         return type(self).__bool__(self)
 
+    def __len__(self):
+        return len(self.dict)
+
 
 class MultiValueDictKeyError(KeyError):
     pass
diff --git a/tests/utils_tests/test_datastructures.py b/tests/utils_tests/test_datastructures.py
index c0ed3435eb..99f7a1d05f 100644
--- a/tests/utils_tests/test_datastructures.py
+++ b/tests/utils_tests/test_datastructures.py
@@ -21,6 +21,14 @@ class OrderedSetTests(SimpleTestCase):
         s.add(1)
         self.assertTrue(s)
 
+    def test_len(self):
+        s = OrderedSet()
+        self.assertEqual(len(s), 0)
+        s.add(1)
+        s.add(2)
+        s.add(2)
+        self.assertEqual(len(s), 2)
+
 
 class MultiValueDictTests(SimpleTestCase):