diff --git a/gtsam/hybrid/MixtureFactor.h b/gtsam/hybrid/MixtureFactor.h
index 5a2383221..511705cf3 100644
--- a/gtsam/hybrid/MixtureFactor.h
+++ b/gtsam/hybrid/MixtureFactor.h
@@ -107,8 +107,12 @@ class MixtureFactor : public HybridFactor {
       std::copy(f->keys().begin(), f->keys().end(),
                 std::inserter(factor_keys_set, factor_keys_set.end()));
 
-      nonlinear_factors.push_back(
-          boost::dynamic_pointer_cast<NonlinearFactor>(f));
+      if (auto nf = boost::dynamic_pointer_cast<NonlinearFactor>(f)) {
+        nonlinear_factors.push_back(nf);
+      } else {
+        throw std::runtime_error(
+            "Factors passed into MixtureFactor need to be nonlinear!");
+      }
     }
     factors_ = Factors(discreteKeys, nonlinear_factors);
 
@@ -125,10 +129,10 @@ class MixtureFactor : public HybridFactor {
    * @brief Compute error of the MixtureFactor as a tree.
    *
    * @param continuousVals The continuous values for which to compute the error.
-   * @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 Values& continuousVals) const {
+  AlgebraicDecisionTree<Key> error(const Values& continuousVals) const {
     // functor to convert from sharedFactor to double error value.
     auto errorFunc = [continuousVals](const sharedFactor& factor) {
       return factor->error(continuousVals);
@@ -165,7 +169,7 @@ class MixtureFactor : public HybridFactor {
 
   /// print to stdout
   void print(
-      const std::string& s = "MixtureFactor",
+      const std::string& s = "",
       const KeyFormatter& keyFormatter = DefaultKeyFormatter) const override {
     std::cout << (s.empty() ? "" : s + " ");
     Base::print("", keyFormatter);