diff --git a/voltha/extensions/omci/omci_messages.py b/voltha/extensions/omci/omci_messages.py
index 2e11136..0fb2125 100644
--- a/voltha/extensions/omci/omci_messages.py
+++ b/voltha/extensions/omci/omci_messages.py
@@ -233,7 +233,7 @@
         ShortField("entity_id", 0),
         ShortField("alarmed_entity_class", None),
         ShortField("alarmed_entity_id", 0),
-        StrFixedLenField("alarm_bit_map", None, 27)  # TODO better type?
+        BitField("alarm_bit_map", None, 224)
     ]