diff --git a/gtsam/hybrid/GaussianMixtureFactor.h b/gtsam/hybrid/GaussianMixtureFactor.h
index ad8e19f02..69149ac05 100644
--- a/gtsam/hybrid/GaussianMixtureFactor.h
+++ b/gtsam/hybrid/GaussianMixtureFactor.h
@@ -62,6 +62,7 @@ class GTSAM_EXPORT GaussianMixtureFactor : public HybridFactor {
       // Note: constant is log of normalization constant for probabilities.
       // Errors is the negative log-likelihood,
       // hence we subtract the constant here.
+      if (!factor) return 0.0;  // If nullptr, return 0.0 error
       return factor->error(values) - constant;
     }
 
diff --git a/gtsam/hybrid/HybridGaussianFactorGraph.cpp b/gtsam/hybrid/HybridGaussianFactorGraph.cpp
index caef85068..0ffc22ba1 100644
--- a/gtsam/hybrid/HybridGaussianFactorGraph.cpp
+++ b/gtsam/hybrid/HybridGaussianFactorGraph.cpp
@@ -199,14 +199,14 @@ hybridElimination(const HybridGaussianFactorGraph &factors,
   DiscreteKeys discreteSeparator(discreteSeparatorSet.begin(),
                                  discreteSeparatorSet.end());
 
-  // Collect all the frontal factors to create Gaussian factor graphs
-  // indexed on the discrete keys.
+  // Collect all the factors to create a set of Gaussian factor graphs in a
+  // decision tree indexed by all discrete keys involved.
   GaussianMixtureFactor::Sum sum = factors.SumFrontals();
 
-  // If a tree leaf contains nullptr,
-  // convert that leaf to an empty GaussianFactorGraph.
-  // Needed since the DecisionTree will otherwise create
-  // a GFG with a single (null) factor.
+  // If a tree leaf contains nullptr, convert that leaf to an empty
+  // GaussianFactorGraph. Needed since the DecisionTree will otherwise create a
+  // GFG with a single (null) factor.
+  // TODO(dellaert): can SumFrontals not guarantee this?
   auto emptyGaussian =
       [](const GaussianMixtureFactor::GraphAndConstant &graph_z) {
         bool hasNull = std::any_of(
@@ -222,7 +222,6 @@ hybridElimination(const HybridGaussianFactorGraph &factors,
   using EliminationPair = std::pair<boost::shared_ptr<GaussianConditional>,
                                     GaussianMixtureFactor::FactorAndConstant>;
 
-  KeyVector keysOfEliminated;  // Not the ordering
   KeyVector keysOfSeparator;
 
   // This is the elimination method on the leaf nodes
@@ -236,24 +235,21 @@ hybridElimination(const HybridGaussianFactorGraph &factors,
     gttic_(hybrid_eliminate);
 #endif
 
-    std::pair<boost::shared_ptr<GaussianConditional>,
-              boost::shared_ptr<GaussianFactor>>
-        conditional_factor =
-            EliminatePreferCholesky(graph_z.graph, frontalKeys);
+    boost::shared_ptr<GaussianConditional> conditional;
+    boost::shared_ptr<GaussianFactor> newFactor;
+    boost::tie(conditional, newFactor) =
+        EliminatePreferCholesky(graph_z.graph, frontalKeys);
 
-    // Initialize the keysOfEliminated to be the keys of the
-    // eliminated GaussianConditional
-    keysOfEliminated = conditional_factor.first->keys();
-    keysOfSeparator = conditional_factor.second->keys();
+    // TODO(dellaert): always the same, and we already computed this in caller?
+    keysOfSeparator = newFactor->keys();
 
 #ifdef HYBRID_TIMING
     gttoc_(hybrid_eliminate);
 #endif
 
-    GaussianConditional::shared_ptr conditional = conditional_factor.first;
     // Get the log of the log normalization constant inverse.
     double logZ = -conditional->logNormalizationConstant() + graph_z.constant;
-    return {conditional, {conditional_factor.second, logZ}};
+    return {conditional, {newFactor, logZ}};
   };
 
   // Perform elimination!
@@ -266,44 +262,31 @@ hybridElimination(const HybridGaussianFactorGraph &factors,
 
   // Separate out decision tree into conditionals and remaining factors.
   auto pair = unzip(eliminationResults);
-  const auto &separatorFactors = pair.second;
 
   // Create the GaussianMixture from the conditionals
   auto conditional = boost::make_shared<GaussianMixture>(
       frontalKeys, keysOfSeparator, discreteSeparator, pair.first);
 
-  // If there are no more continuous parents, then we should create here a
-  // DiscreteFactor, with the error for each discrete choice.
+  // If there are no more continuous parents, then we should create a
+  // DiscreteFactor here, with the error for each discrete choice.
+  const auto &separatorFactors = pair.second;
   if (keysOfSeparator.empty()) {
     auto factorProb =
         [&](const GaussianMixtureFactor::FactorAndConstant &factor_z) {
-          GaussianFactor::shared_ptr factor = factor_z.factor;
-          if (!factor) {
-            return 0.0;  // If nullptr, return 0.0 probability
-          } else {
-            // This is the probability q(μ) at the MLE point.
-            double error = factor_z.error(VectorValues());
-            return std::exp(-error);
-          }
+          // This is the probability q(μ) at the MLE point.
+          return factor_z.error(VectorValues());
         };
-    DecisionTree<Key, double> fdt(separatorFactors, factorProb);
-    // Normalize the values of decision tree to be valid probabilities
-    double sum = 0.0;
-    auto visitor = [&](double y) { sum += y; };
-    fdt.visit(visitor);
-    // fdt = DecisionTree<Key, double>(fdt,
-    //                                 [sum](const double &x) { return x / sum;
-    //                                 });
-
-    auto discreteFactor =
+    const DecisionTree<Key, double> fdt(separatorFactors, factorProb);
+    const auto discreteFactor =
         boost::make_shared<DecisionTreeFactor>(discreteSeparator, fdt);
 
     return {boost::make_shared<HybridConditional>(conditional),
             boost::make_shared<HybridDiscreteFactor>(discreteFactor)};
-
   } else {
     // Create a resulting GaussianMixtureFactor on the separator.
-    auto factor = boost::make_shared<GaussianMixtureFactor>(
+    // Keys can be computed from the factors, so we should not need to pass them
+    // in.
+    const auto factor = boost::make_shared<GaussianMixtureFactor>(
         KeyVector(continuousSeparator.begin(), continuousSeparator.end()),
         discreteSeparator, separatorFactors);
     return {boost::make_shared<HybridConditional>(conditional), factor};