diff --git a/gtsam/hybrid/HybridBayesNet.cpp b/gtsam/hybrid/HybridBayesNet.cpp
index e72e16c45..7a46d7832 100644
--- a/gtsam/hybrid/HybridBayesNet.cpp
+++ b/gtsam/hybrid/HybridBayesNet.cpp
@@ -236,7 +236,7 @@ VectorValues HybridBayesNet::optimize(const DiscreteValues &assignment) const {
 }
 
 /* ************************************************************************* */
-HybridValues HybridBayesNet::sample(HybridValues &given,
+HybridValues HybridBayesNet::sample(const HybridValues &given,
                                     std::mt19937_64 *rng) const {
   DiscreteBayesNet dbn;
   for (auto &&conditional : *this) {
@@ -261,7 +261,7 @@ HybridValues HybridBayesNet::sample(std::mt19937_64 *rng) const {
 }
 
 /* ************************************************************************* */
-HybridValues HybridBayesNet::sample(HybridValues &given) const {
+HybridValues HybridBayesNet::sample(const HybridValues &given) const {
   return sample(given, &kRandomNumberGenerator);
 }
 
diff --git a/gtsam/hybrid/HybridBayesNet.h b/gtsam/hybrid/HybridBayesNet.h
index 3412aaf78..1e6bebf1a 100644
--- a/gtsam/hybrid/HybridBayesNet.h
+++ b/gtsam/hybrid/HybridBayesNet.h
@@ -132,7 +132,7 @@ class GTSAM_EXPORT HybridBayesNet : public BayesNet<HybridConditional> {
    * @param rng The pseudo-random number generator.
    * @return HybridValues
    */
-  HybridValues sample(HybridValues& given, std::mt19937_64 *rng) const;
+  HybridValues sample(const HybridValues &given, std::mt19937_64 *rng) const;
 
   /**
    * @brief Sample using ancestral sampling.
@@ -152,7 +152,7 @@ class GTSAM_EXPORT HybridBayesNet : public BayesNet<HybridConditional> {
    * @param given Values of missing variables.
    * @return HybridValues
    */
-  HybridValues sample(HybridValues& given) const;
+  HybridValues sample(const HybridValues &given) const;
 
   /**
    * @brief Sample using ancestral sampling, use default rng.