diff --git a/gtsam/hybrid/HybridBayesNet.h b/gtsam/hybrid/HybridBayesNet.h
index e84103a50..f28224d37 100644
--- a/gtsam/hybrid/HybridBayesNet.h
+++ b/gtsam/hybrid/HybridBayesNet.h
@@ -73,6 +73,8 @@ class GTSAM_EXPORT HybridBayesNet : public BayesNet<HybridConditional> {
         HybridConditional(boost::make_shared<DiscreteConditional>(key, table)));
   }
 
+  using Base::push_back;
+
   /// Get a specific Gaussian mixture by index `i`.
   GaussianMixture::shared_ptr atMixture(size_t i) const;
 
diff --git a/gtsam/hybrid/HybridFactorGraph.h b/gtsam/hybrid/HybridFactorGraph.h
index fc730f0c9..05a17b000 100644
--- a/gtsam/hybrid/HybridFactorGraph.h
+++ b/gtsam/hybrid/HybridFactorGraph.h
@@ -135,6 +135,28 @@ class HybridFactorGraph : public FactorGraph<HybridFactor> {
       push_hybrid(p);
     }
   }
+
+  /// Get all the discrete keys in the factor graph.
+  const KeySet discreteKeys() const {
+    KeySet discrete_keys;
+    for (auto& factor : factors_) {
+      for (const DiscreteKey& k : factor->discreteKeys()) {
+        discrete_keys.insert(k.first);
+      }
+    }
+    return discrete_keys;
+  }
+
+  /// Get all the continuous keys in the factor graph.
+  const KeySet continuousKeys() const {
+    KeySet keys;
+    for (auto& factor : factors_) {
+      for (const Key& key : factor->continuousKeys()) {
+        keys.insert(key);
+      }
+    }
+    return keys;
+  }
 };
 
 }  // namespace gtsam
diff --git a/gtsam/hybrid/HybridGaussianFactorGraph.cpp b/gtsam/hybrid/HybridGaussianFactorGraph.cpp
index 09b592bd6..ddb776ff4 100644
--- a/gtsam/hybrid/HybridGaussianFactorGraph.cpp
+++ b/gtsam/hybrid/HybridGaussianFactorGraph.cpp
@@ -404,31 +404,9 @@ void HybridGaussianFactorGraph::add(DecisionTreeFactor::shared_ptr factor) {
   FactorGraph::add(boost::make_shared<HybridDiscreteFactor>(factor));
 }
 
-/* ************************************************************************ */
-const KeySet HybridGaussianFactorGraph::getDiscreteKeys() const {
-  KeySet discrete_keys;
-  for (auto &factor : factors_) {
-    for (const DiscreteKey &k : factor->discreteKeys()) {
-      discrete_keys.insert(k.first);
-    }
-  }
-  return discrete_keys;
-}
-
-/* ************************************************************************ */
-const KeySet HybridGaussianFactorGraph::getContinuousKeys() const {
-  KeySet keys;
-  for (auto &factor : factors_) {
-    for (const Key &key : factor->continuousKeys()) {
-      keys.insert(key);
-    }
-  }
-  return keys;
-}
-
 /* ************************************************************************ */
 const Ordering HybridGaussianFactorGraph::getHybridOrdering() const {
-  KeySet discrete_keys = getDiscreteKeys();
+  KeySet discrete_keys = discreteKeys();
   for (auto &factor : factors_) {
     for (const DiscreteKey &k : factor->discreteKeys()) {
       discrete_keys.insert(k.first);
diff --git a/gtsam/hybrid/HybridGaussianFactorGraph.h b/gtsam/hybrid/HybridGaussianFactorGraph.h
index ad5cde09b..bd24cdeaa 100644
--- a/gtsam/hybrid/HybridGaussianFactorGraph.h
+++ b/gtsam/hybrid/HybridGaussianFactorGraph.h
@@ -161,12 +161,6 @@ class GTSAM_EXPORT HybridGaussianFactorGraph
     }
   }
 
-  /// Get all the discrete keys in the factor graph.
-  const KeySet getDiscreteKeys() const;
-
-  /// Get all the continuous keys in the factor graph.
-  const KeySet getContinuousKeys() const;
-
   /**
    * @brief Return a Colamd constrained ordering where the discrete keys are
    * eliminated after the continuous keys.
diff --git a/gtsam/hybrid/HybridGaussianISAM.cpp b/gtsam/hybrid/HybridGaussianISAM.cpp
index 6946775b9..57e50104d 100644
--- a/gtsam/hybrid/HybridGaussianISAM.cpp
+++ b/gtsam/hybrid/HybridGaussianISAM.cpp
@@ -62,23 +62,24 @@ void HybridGaussianISAM::updateInternal(
   for (const sharedClique& orphan : *orphans)
     factors += boost::make_shared<BayesTreeOrphanWrapper<Node> >(orphan);
 
-  KeySet allDiscrete;
-  for (auto& factor : factors) {
-    for (auto& k : factor->discreteKeys()) {
-      allDiscrete.insert(k.first);
-    }
-  }
+  // Get all the discrete keys from the factors
+  KeySet allDiscrete = factors.discreteKeys();
+
+  // Create KeyVector with continuous keys followed by discrete keys.
   KeyVector newKeysDiscreteLast;
+  // Insert continuous keys first.
   for (auto& k : newFactorKeys) {
     if (!allDiscrete.exists(k)) {
       newKeysDiscreteLast.push_back(k);
     }
   }
+  // Insert discrete keys at the end
   std::copy(allDiscrete.begin(), allDiscrete.end(),
             std::back_inserter(newKeysDiscreteLast));
 
   // Get an ordering where the new keys are eliminated last
   const VariableIndex index(factors);
+
   Ordering elimination_ordering;
   if (ordering) {
     elimination_ordering = *ordering;
diff --git a/gtsam/hybrid/tests/testHybridBayesNet.cpp b/gtsam/hybrid/tests/testHybridBayesNet.cpp
index 0c15ee83d..cc2ab1759 100644
--- a/gtsam/hybrid/tests/testHybridBayesNet.cpp
+++ b/gtsam/hybrid/tests/testHybridBayesNet.cpp
@@ -52,6 +52,21 @@ TEST(HybridBayesNet, Creation) {
   EXPECT(df.equals(expected));
 }
 
+/* ****************************************************************************/
+// Test adding a bayes net to another one.
+TEST(HybridBayesNet, Add) {
+  HybridBayesNet bayesNet;
+
+  bayesNet.add(Asia, "99/1");
+
+  DiscreteConditional expected(Asia, "99/1");
+
+  HybridBayesNet other;
+  other.push_back(bayesNet);
+  EXPECT(bayesNet.equals(other));
+}
+
+
 /* ****************************************************************************/
 // Test choosing an assignment of conditionals
 TEST(HybridBayesNet, Choose) {
diff --git a/gtsam/hybrid/tests/testHybridIncremental.cpp b/gtsam/hybrid/tests/testHybridGaussianISAM.cpp
similarity index 100%
rename from gtsam/hybrid/tests/testHybridIncremental.cpp
rename to gtsam/hybrid/tests/testHybridGaussianISAM.cpp