diff --git a/gtsam/hybrid/GaussianMixtureFactor.cpp b/gtsam/hybrid/GaussianMixtureFactor.cpp
index 181b1e6a5..a8500911a 100644
--- a/gtsam/hybrid/GaussianMixtureFactor.cpp
+++ b/gtsam/hybrid/GaussianMixtureFactor.cpp
@@ -95,4 +95,16 @@ GaussianMixtureFactor::Sum GaussianMixtureFactor::asGaussianFactorGraphTree()
   };
   return {factors_, wrap};
 }
+
+/* *******************************************************************************/
+AlgebraicDecisionTree<Key> GaussianMixtureFactor::error(
+    const VectorValues &continuousVals) const {
+  // functor to convert from sharedFactor to double error value.
+  auto errorFunc = [continuousVals](const GaussianFactor::shared_ptr &factor) {
+    return factor->error(continuousVals);
+  };
+  DecisionTree<Key, double> errorTree(factors_, errorFunc);
+  return errorTree;
+}
+
 }  // namespace gtsam
diff --git a/gtsam/hybrid/GaussianMixtureFactor.h b/gtsam/hybrid/GaussianMixtureFactor.h
index f27c49180..31ec3c1a0 100644
--- a/gtsam/hybrid/GaussianMixtureFactor.h
+++ b/gtsam/hybrid/GaussianMixtureFactor.h
@@ -20,6 +20,7 @@
 
 #pragma once
 
+#include <gtsam/discrete/AlgebraicDecisionTree.h>
 #include <gtsam/discrete/DecisionTree.h>
 #include <gtsam/discrete/DiscreteKey.h>
 #include <gtsam/hybrid/HybridGaussianFactor.h>
@@ -131,17 +132,10 @@ class GTSAM_EXPORT GaussianMixtureFactor : public HybridFactor {
    * @brief Compute error of the GaussianMixtureFactor as a tree.
    *
    * @param continuousVals The continuous VectorValues.
-   * @return DecisionTree<Key, double> A decision tree with corresponding keys
+   * @return AlgebraicDecisionTree<Key> A decision tree with corresponding keys
    * as the factor but leaf values as the error.
    */
-  DecisionTree<Key, double> error(const VectorValues &c) const {
-    // functor to convert from sharedFactor to double error value.
-    auto errorFunc = [c](const GaussianFactor::shared_ptr &factor) {
-      return factor->error(c);
-    };
-    DecisionTree<Key, double> errorTree(factors_, errorFunc);
-    return errorTree;
-  }
+  AlgebraicDecisionTree<Key> error(const VectorValues &continuousVals) const;
 
   /// Add MixtureFactor to a Sum, syntactic sugar.
   friend Sum &operator+=(Sum &sum, const GaussianMixtureFactor &factor) {
diff --git a/gtsam/hybrid/tests/testGaussianMixtureFactor.cpp b/gtsam/hybrid/tests/testGaussianMixtureFactor.cpp
index cb9068c30..e6248f5c9 100644
--- a/gtsam/hybrid/tests/testGaussianMixtureFactor.cpp
+++ b/gtsam/hybrid/tests/testGaussianMixtureFactor.cpp
@@ -10,7 +10,7 @@
  * -------------------------------------------------------------------------- */
 
 /**
- * @file    GaussianMixtureFactor.cpp
+ * @file    testGaussianMixtureFactor.cpp
  * @brief   Unit tests for GaussianMixtureFactor
  * @author  Varun Agrawal
  * @author  Fan Jiang
@@ -135,7 +135,7 @@ TEST(GaussianMixtureFactor, Printing) {
   EXPECT(assert_print_equal(expected, mixtureFactor));
 }
 
-TEST_UNSAFE(GaussianMixtureFactor, GaussianMixture) {
+TEST(GaussianMixtureFactor, GaussianMixture) {
   KeyVector keys;
   keys.push_back(X(0));
   keys.push_back(X(1));
@@ -151,6 +151,39 @@ TEST_UNSAFE(GaussianMixtureFactor, GaussianMixture) {
   EXPECT_LONGS_EQUAL(2, gm.discreteKeys().size());
 }
 
+/* ************************************************************************* */
+// Test the error of the GaussianMixtureFactor
+TEST(GaussianMixtureFactor, Error) {
+  DiscreteKey m1(1, 2);
+
+  auto A01 = Matrix2::Identity();
+  auto A02 = Matrix2::Identity();
+
+  auto A11 = Matrix2::Identity();
+  auto A12 = Matrix2::Identity() * 2;
+
+  auto b = Vector2::Zero();
+
+  auto f0 = boost::make_shared<JacobianFactor>(X(1), A01, X(2), A02, b);
+  auto f1 = boost::make_shared<JacobianFactor>(X(1), A11, X(2), A12, b);
+  std::vector<GaussianFactor::shared_ptr> factors{f0, f1};
+
+  GaussianMixtureFactor mixtureFactor({X(1), X(2)}, {m1}, factors);
+
+  VectorValues continuousVals;
+  continuousVals.insert(X(1), Vector2(0, 0));
+  continuousVals.insert(X(2), Vector2(1, 1));
+
+  // error should return a tree of errors, with nodes for each discrete value.
+  AlgebraicDecisionTree<Key> error_tree = mixtureFactor.error(continuousVals);
+
+  std::vector<DiscreteKey> discrete_keys = {m1};
+  std::vector<double> errors = {1, 4};
+  AlgebraicDecisionTree<Key> expected_error(discrete_keys, errors);
+
+  EXPECT(assert_equal(expected_error, error_tree));
+}
+
 /* ************************************************************************* */
 int main() {
   TestResult tr;