diff --git a/gtsam/hybrid/HybridGaussianFactorGraph.cpp b/gtsam/hybrid/HybridGaussianFactorGraph.cpp
index 3732f6705..dbf480733 100644
--- a/gtsam/hybrid/HybridGaussianFactorGraph.cpp
+++ b/gtsam/hybrid/HybridGaussianFactorGraph.cpp
@@ -98,7 +98,9 @@ GaussianFactorGraphTree HybridGaussianFactorGraph::assembleGraphTree() const {
 
   for (auto &f : factors_) {
     // TODO(dellaert): just use a virtual method defined in HybridFactor.
-    if (auto gm = dynamic_pointer_cast<GaussianMixtureFactor>(f)) {
+    if (auto gf = dynamic_pointer_cast<GaussianFactor>(f)) {
+      result = addGaussian(result, gf);
+    } else if (auto gm = dynamic_pointer_cast<GaussianMixtureFactor>(f)) {
       result = gm->add(result);
     } else if (auto hc = dynamic_pointer_cast<HybridConditional>(f)) {
       if (auto gm = hc->asMixture()) {
@@ -107,6 +109,7 @@ GaussianFactorGraphTree HybridGaussianFactorGraph::assembleGraphTree() const {
         result = addGaussian(result, g);
       } else {
         // Has to be discrete.
+        // TODO(dellaert): in C++20, we can use std::visit.
         continue;
       }
     } else if (auto gf = dynamic_pointer_cast<HybridGaussianFactor>(f)) {
@@ -486,7 +489,7 @@ AlgebraicDecisionTree<Key> HybridGaussianFactorGraph::error(
       // If factor at `idx` is discrete-only, we skip.
       continue;
     } else {
-      throwRuntimeError("HybridGaussianFactorGraph::error", f);
+      throwRuntimeError("HybridGaussianFactorGraph::error(VV)", f);
     }
   }
 
@@ -497,13 +500,15 @@ AlgebraicDecisionTree<Key> HybridGaussianFactorGraph::error(
 double HybridGaussianFactorGraph::error(const HybridValues &values) const {
   double error = 0.0;
   for (auto &f : factors_) {
-    if (auto hf = dynamic_pointer_cast<HybridFactor>(f)) {
+    if (auto hf = dynamic_pointer_cast<GaussianFactor>(f)) {
+      error += hf->error(values.continuous());
+    } else if (auto hf = dynamic_pointer_cast<HybridFactor>(f)) {
       // TODO(dellaert): needs to change when we discard other wrappers.
       error += hf->error(values);
     } else if (auto dtf = dynamic_pointer_cast<DecisionTreeFactor>(f)) {
       error -= log((*dtf)(values.discrete()));
     } else {
-      throwRuntimeError("HybridGaussianFactorGraph::error", f);
+      throwRuntimeError("HybridGaussianFactorGraph::error(HV)", f);
     }
   }
   return error;