diff --git a/voltha/extensions/omci/omci_entities.py b/voltha/extensions/omci/omci_entities.py
index 8a919f3..868c89c 100644
--- a/voltha/extensions/omci/omci_entities.py
+++ b/voltha/extensions/omci/omci_entities.py
@@ -51,8 +51,8 @@
 
     class_id = 'to be filled by subclass'
     attributes = []
-    mandatory_operations = {}
-    optional_operations = {}
+    mandatory_operations = set()
+    optional_operations = set()
 
     # will be map of attr_name -> index in attributes, initialized by metaclass
     attribute_name_to_index_map = None