diff --git a/capa/features/freeze.py b/capa/features/freeze.py
index ca0b729b..f90959f5 100644
--- a/capa/features/freeze.py
+++ b/capa/features/freeze.py
@@ -67,6 +67,7 @@ def serialize_feature(feature):
 
 
 KNOWN_FEATURES = {F.__name__: F for F in capa.features.common.Feature.__subclasses__()}
+KNOWN_FEATURES.update({F.__name__: F for F in capa.features.insn._Operand.__subclasses__()})
 
 
 def deserialize_feature(doc):