diff --git a/gtsam/hybrid/GaussianMixture.cpp b/gtsam/hybrid/GaussianMixture.cpp
index c0815b2d7..82d16226a 100644
--- a/gtsam/hybrid/GaussianMixture.cpp
+++ b/gtsam/hybrid/GaussianMixture.cpp
@@ -36,7 +36,7 @@ GaussianMixture::GaussianMixture(
       conditionals_(conditionals) {}
 
 /* *******************************************************************************/
-const GaussianMixture::Conditionals &GaussianMixture::conditionals() {
+const GaussianMixture::Conditionals &GaussianMixture::conditionals() const {
   return conditionals_;
 }
 
diff --git a/gtsam/hybrid/GaussianMixture.h b/gtsam/hybrid/GaussianMixture.h
index 88d5a02c0..a3393dbb0 100644
--- a/gtsam/hybrid/GaussianMixture.h
+++ b/gtsam/hybrid/GaussianMixture.h
@@ -142,7 +142,7 @@ class GTSAM_EXPORT GaussianMixture
   /// @}
 
   /// Getter for the underlying Conditionals DecisionTree
-  const Conditionals &conditionals();
+  const Conditionals &conditionals() const;
 
   /**
    * @brief Compute error of the GaussianMixture as a tree.