diff --git a/python/mozbuild/mozbuild/test/test_util.py b/python/mozbuild/mozbuild/test/test_util.py
index 486a7f22a2f..b9972a219fe 100644
--- a/python/mozbuild/mozbuild/test/test_util.py
+++ b/python/mozbuild/mozbuild/test/test_util.py
@@ -370,6 +370,13 @@ class TestStrictOrderingOnAppendListWithFlagsFactory(unittest.TestCase):
         with self.assertRaises(AttributeError):
             l['b'].baz = False
 
+        l['b'].update(foo=False, bar=12)
+        self.assertEqual(l['b'].foo, False)
+        self.assertEqual(l['b'].bar, 12)
+
+        with self.assertRaises(AttributeError):
+            l['b'].update(xyz=1)
+
 
 class TestHierarchicalStringListWithFlagsFactory(unittest.TestCase):
     def test_hierarchical_string_list_with_flags_factory(self):
diff --git a/python/mozbuild/mozbuild/util.py b/python/mozbuild/mozbuild/util.py
index cebb26ad5cd..30c57e6803a 100644
--- a/python/mozbuild/mozbuild/util.py
+++ b/python/mozbuild/mozbuild/util.py
@@ -375,6 +375,10 @@ def FlagsFactory(flags):
         __slots__ = flags.keys()
         _flags = flags
 
+        def update(self, **kwargs):
+            for k, v in kwargs.iteritems():
+                setattr(self, k, v)
+
         def __getattr__(self, name):
             if name not in self.__slots__:
                 raise AttributeError("'%s' object has no attribute '%s'" %