diff --git a/gtsam/hybrid/HybridGaussianFactorGraph.cpp b/gtsam/hybrid/HybridGaussianFactorGraph.cpp
index b5344a988..caef85068 100644
--- a/gtsam/hybrid/HybridGaussianFactorGraph.cpp
+++ b/gtsam/hybrid/HybridGaussianFactorGraph.cpp
@@ -59,8 +59,9 @@ namespace gtsam {
 template class EliminateableFactorGraph<HybridGaussianFactorGraph>;
 
 /* ************************************************************************ */
-static GaussianMixtureFactor::Sum &addGaussian(
-    GaussianMixtureFactor::Sum &sum, const GaussianFactor::shared_ptr &factor) {
+static GaussianMixtureFactor::Sum addGaussian(
+    const GaussianMixtureFactor::Sum &sum,
+    const GaussianFactor::shared_ptr &factor) {
   // If the decision tree is not initialized, then initialize it.
   if (sum.empty()) {
     GaussianFactorGraph result;
diff --git a/gtsam/hybrid/tests/testHybridEstimation.cpp b/gtsam/hybrid/tests/testHybridEstimation.cpp
index e29e07afa..d457d039f 100644
--- a/gtsam/hybrid/tests/testHybridEstimation.cpp
+++ b/gtsam/hybrid/tests/testHybridEstimation.cpp
@@ -500,7 +500,7 @@ TEST(HybridEstimation, CorrectnessViaSampling) {
   const HybridValues sample = bn->sample(&rng);
   double expected_ratio = compute_ratio(sample);
   // regression
-  // EXPECT_DOUBLES_EQUAL(1.9477340410546764, ratio, 1e-9);
+  EXPECT_DOUBLES_EQUAL(1.9477340410546764, expected_ratio, 1e-9);
 
   // 3. Do sampling
   constexpr int num_samples = 10;