diff --git a/components/style/properties/data.py b/components/style/properties/data.py
index ac1de39f877..9c085d20509 100644
--- a/components/style/properties/data.py
+++ b/components/style/properties/data.py
@@ -584,6 +584,7 @@ class Alias(object):
         self.gecko_pref = gecko_pref
         self.transitionable = original.transitionable
         self.rule_types_allowed = original.rule_types_allowed
+        self.flags = original.flags
 
     @staticmethod
     def type():