diff --git a/gtsam/hybrid/GaussianMixture.cpp b/gtsam/hybrid/GaussianMixture.cpp
index fa4248921..325c32f95 100644
--- a/gtsam/hybrid/GaussianMixture.cpp
+++ b/gtsam/hybrid/GaussianMixture.cpp
@@ -330,19 +330,28 @@ AlgebraicDecisionTree<Key> GaussianMixture::logProbability(
   return DecisionTree<Key, double>(conditionals_, probFunc);
 }
 
+/* ************************************************************************* */
+double GaussianMixture::conditionalError(
+    const GaussianConditional::shared_ptr &conditional,
+    const VectorValues &continuousValues) const {
+  // Check if valid pointer
+  if (conditional) {
+    return conditional->error(continuousValues) +  //
+           logConstant_ - conditional->logNormalizationConstant();
+  } else {
+    // If not valid, pointer, it means this conditional was pruned,
+    // so we return maximum error.
+    // This way the negative exponential will give
+    // a probability value close to 0.0.
+    return std::numeric_limits<double>::max();
+  }
+}
+
 /* *******************************************************************************/
 AlgebraicDecisionTree<Key> GaussianMixture::errorTree(
     const VectorValues &continuousValues) const {
   auto errorFunc = [&](const GaussianConditional::shared_ptr &conditional) {
-    // Check if valid pointer
-    if (conditional) {
-      return conditional->error(continuousValues) +  //
-             logConstant_ - conditional->logNormalizationConstant();
-    } else {
-      // If not valid, pointer, it means this conditional was pruned,
-      // so we return maximum error.
-      return std::numeric_limits<double>::max();
-    }
+    return conditionalError(conditional, continuousValues);
   };
   DecisionTree<Key, double> error_tree(conditionals_, errorFunc);
   return error_tree;
@@ -350,33 +359,9 @@ AlgebraicDecisionTree<Key> GaussianMixture::errorTree(
 
 /* *******************************************************************************/
 double GaussianMixture::error(const HybridValues &values) const {
-  // Check if discrete keys in discrete assignment are
-  // present in the GaussianMixture
-  KeyVector dKeys = this->discreteKeys_.indices();
-  bool valid_assignment = false;
-  for (auto &&kv : values.discrete()) {
-    if (std::find(dKeys.begin(), dKeys.end(), kv.first) != dKeys.end()) {
-      valid_assignment = true;
-      break;
-    }
-  }
-
-  // The discrete assignment is not valid so we throw an error.
-  if (!valid_assignment) {
-    throw std::runtime_error(
-        "Invalid discrete values in values. Not all discrete keys specified.");
-  }
-
   // Directly index to get the conditional, no need to build the whole tree.
   auto conditional = conditionals_(values.discrete());
-  if (conditional) {
-    return conditional->error(values.continuous()) +  //
-           logConstant_ - conditional->logNormalizationConstant();
-  } else {
-    // If not valid, pointer, it means this conditional was pruned,
-    // so we return maximum error.
-    return std::numeric_limits<double>::max();
-  }
+  return conditionalError(conditional, values.continuous());
 }
 
 /* *******************************************************************************/
diff --git a/gtsam/hybrid/GaussianMixture.h b/gtsam/hybrid/GaussianMixture.h
index 41692bb1c..714c00272 100644
--- a/gtsam/hybrid/GaussianMixture.h
+++ b/gtsam/hybrid/GaussianMixture.h
@@ -256,6 +256,10 @@ class GTSAM_EXPORT GaussianMixture
   /// Check whether `given` has values for all frontal keys.
   bool allFrontalsGiven(const VectorValues &given) const;
 
+  /// Helper method to compute the error of a conditional.
+  double conditionalError(const GaussianConditional::shared_ptr &conditional,
+                          const VectorValues &continuousValues) const;
+
 #ifdef GTSAM_ENABLE_BOOST_SERIALIZATION
   /** Serialization function */
   friend class boost::serialization::access;