diff --git a/djcelery_transactions/transaction_signals.py b/djcelery_transactions/transaction_signals.py
index d9b1c67..07553db 100644
--- a/djcelery_transactions/transaction_signals.py
+++ b/djcelery_transactions/transaction_signals.py
@@ -80,7 +80,7 @@ def leave_transaction_management(old_function, *args, **kwargs):
 def managed(old_function, *args, **kwargs):
     # Turning transaction management off causes the current transaction to be
     # committed if it's dirty. We must send the signal after the actual commit.
-    flag = kwargs.get('flag', args[0])
+    flag = kwargs.get('flag', args[0] if args else None)
     if state is not None:
         using = kwargs.get('using', args[1] if len(args) > 1 else None)
         # Do not commit too early for prior versions of Django 1.3
diff --git a/tests/tests.py b/tests/tests.py
index 04ea8ef..a0d01ca 100644
--- a/tests/tests.py
+++ b/tests/tests.py
@@ -47,3 +47,17 @@ def do_something():
             self.assertFalse(my_global)
         else:
             self.fail('Exception not raised')
+
+    def test_django_db_transaction_managed(self):
+        """
+        Check that django.db.transaction.managed is not affected
+        by monkey-patching
+        """
+        from django.db import transaction
+        self.assertFalse(transaction.is_managed())
+        transaction.enter_transaction_management()
+        try:
+            transaction.managed()
+            self.assertTrue(transaction.is_managed())
+        finally:
+            transaction.leave_transaction_management()