diff --git a/gtsam/hybrid/HybridConditional.h b/gtsam/hybrid/HybridConditional.h
index 96ea6d969..b43bb9945 100644
--- a/gtsam/hybrid/HybridConditional.h
+++ b/gtsam/hybrid/HybridConditional.h
@@ -178,6 +178,15 @@ class GTSAM_EXPORT HybridConditional
   /// Get the type-erased pointer to the inner type
   boost::shared_ptr<Factor> inner() { return inner_; }
 
+ private:
+  /** Serialization function */
+  friend class boost::serialization::access;
+  template <class Archive>
+  void serialize(Archive& ar, const unsigned int /*version*/) {
+    ar& BOOST_SERIALIZATION_BASE_OBJECT_NVP(BaseFactor);
+    ar& BOOST_SERIALIZATION_BASE_OBJECT_NVP(BaseConditional);
+  }
+
 };  // HybridConditional
 
 // traits
diff --git a/gtsam/hybrid/HybridFactor.h b/gtsam/hybrid/HybridFactor.h
index 13dc2e6e6..b3cdc231b 100644
--- a/gtsam/hybrid/HybridFactor.h
+++ b/gtsam/hybrid/HybridFactor.h
@@ -47,6 +47,7 @@ class GTSAM_EXPORT HybridFactor : public Factor {
   bool isContinuous_ = false;
   bool isHybrid_ = false;
 
+  // TODO(Varun) remove
   size_t nrContinuous_ = 0;
 
  protected:
@@ -129,6 +130,19 @@ class GTSAM_EXPORT HybridFactor : public Factor {
   const KeyVector &continuousKeys() const { return continuousKeys_; }
 
   /// @}
+
+ private:
+  /** Serialization function */
+  friend class boost::serialization::access;
+  template <class ARCHIVE>
+  void serialize(ARCHIVE &ar, const unsigned int /*version*/) {
+    ar &BOOST_SERIALIZATION_BASE_OBJECT_NVP(Base);
+    ar &BOOST_SERIALIZATION_NVP(isDiscrete_);
+    ar &BOOST_SERIALIZATION_NVP(isContinuous_);
+    ar &BOOST_SERIALIZATION_NVP(isHybrid_);
+    ar &BOOST_SERIALIZATION_NVP(discreteKeys_);
+    ar &BOOST_SERIALIZATION_NVP(continuousKeys_);
+  }
 };
 // HybridFactor