diff --git a/gtsam/hybrid/HybridConditional.h b/gtsam/hybrid/HybridConditional.h
index a34d01388..da7c1421e 100644
--- a/gtsam/hybrid/HybridConditional.h
+++ b/gtsam/hybrid/HybridConditional.h
@@ -187,6 +187,7 @@ class GTSAM_EXPORT HybridConditional
   void serialize(Archive& ar, const unsigned int /*version*/) {
     ar& BOOST_SERIALIZATION_BASE_OBJECT_NVP(BaseFactor);
     ar& BOOST_SERIALIZATION_BASE_OBJECT_NVP(BaseConditional);
+    ar& BOOST_SERIALIZATION_NVP(inner_);
   }
 
 };  // HybridConditional