diff --git a/entity.py b/entity.py
index 713c248..a16c090 100644
--- a/entity.py
+++ b/entity.py
@@ -507,9 +507,9 @@ def get_class_properties(Class):
   def INDIRECT_get_class_properties(Class):
     l = set()
     for r in _inherited_properties_value_restrictions(Class, None, set()):
-      if   r.property._class_property_some and ((r.type == VALUE) or (r.type == SOME) or ((r.type == EXACTLY) and r.cardinality >= 1) or ((r.type == MIN) and r.cardinality >= 1)):
+      if   getattr(r.property, "_class_property_some", False) and ((r.type == VALUE) or (r.type == SOME) or ((r.type == EXACTLY) and r.cardinality >= 1) or ((r.type == MIN) and r.cardinality >= 1)):
         l.add(r.property)
-      elif r.property._class_property_only and  (r.type == ONLY):
+      elif getattr(r.property, "_class_property_only", False) and  (r.type == ONLY):
         l.add(r.property)
         
     for storid in Class.namespace.world._get_triples_s_p(Class.storid):