diff --git a/lib/objects.py b/lib/objects.py
index 0d409cc5c8751781b3af1767835346edb050ee6d..1314e8872a1584c69688152b8b2eeec27bee74a3 100644
--- a/lib/objects.py
+++ b/lib/objects.py
@@ -152,6 +152,8 @@ class TaggableObject(object):
   """An generic class supporting tags.
 
   """
+  __slots__ = []
+
   @staticmethod
   def ValidateTag(tag):
     """Check if a tag is valid.