diff --git a/gtsam/discrete/AlgebraicDecisionTree.h b/gtsam/discrete/AlgebraicDecisionTree.h
index 7e046199a..637f56066 100644
--- a/gtsam/discrete/AlgebraicDecisionTree.h
+++ b/gtsam/discrete/AlgebraicDecisionTree.h
@@ -29,6 +29,18 @@ namespace gtsam {
    */
   template<typename L>
   class GTSAM_EXPORT AlgebraicDecisionTree: public DecisionTree<L, double> {
+    /**
+     * @brief Default method used by `labelFormatter` or `valueFormatter` when printing.
+     * 
+     * @param x The value passed to format.
+     * @return std::string 
+     */
+    static std::string DefaultFormatter(const L& x) {
+      std::stringstream ss;
+      ss << x;
+      return ss.str();
+    }
+
    public:
 
     using Base = DecisionTree<L, double>;
@@ -149,7 +161,7 @@ namespace gtsam {
     /// print method customized to node type `double`.
     void print(const std::string& s,
                const typename Base::LabelFormatter& labelFormatter =
-                   &Base::DefaultFormatter) const {
+                   &DefaultFormatter) const {
       auto valueFormatter = [](const double& v) {
         return (boost::format("%4.2g") % v).str();
       };
diff --git a/gtsam/discrete/DecisionTree.h b/gtsam/discrete/DecisionTree.h
index 0717405dd..6aa97d8ac 100644
--- a/gtsam/discrete/DecisionTree.h
+++ b/gtsam/discrete/DecisionTree.h
@@ -45,18 +45,6 @@ namespace gtsam {
       return a == b;
     }
 
-    /**
-     * @brief Default method used by `labelFormatter` or `valueFormatter` when printing.
-     * 
-     * @param x The value passed to format.
-     * @return std::string 
-     */
-    static std::string DefaultFormatter(const L& x) {
-      std::stringstream ss;
-      ss << x;
-      return ss.str();
-    }
-
   public:
 
     using LabelFormatter = std::function<std::string(L)>;
@@ -101,14 +89,12 @@ namespace gtsam {
       const void* id() const { return this; }
 
       // everything else is virtual, no documentation here as internal
-      virtual void print(
-          const std::string& s,
-          const LabelFormatter& labelFormatter = &DefaultFormatter,
-          const ValueFormatter& valueFormatter = &DefaultFormatter) const = 0;
-      virtual void dot(std::ostream& os,
-                       const LabelFormatter& labelFormatter = &DefaultFormatter,
-                       const ValueFormatter& valueFormatter = &DefaultFormatter,
-                       bool showZero = true) const = 0;
+      virtual void print(const std::string& s,
+                         const LabelFormatter& labelFormatter,
+                         const ValueFormatter& valueFormatter) const = 0;
+      virtual void dot(std::ostream& os, const LabelFormatter& labelFormatter,
+                       const ValueFormatter& valueFormatter,
+                       bool showZero) const = 0;
       virtual bool sameLeaf(const Leaf& q) const = 0;
       virtual bool sameLeaf(const Node& q) const = 0;
       virtual bool equals(const Node& other, const CompareFunc& compare =
@@ -219,9 +205,8 @@ namespace gtsam {
      * @param labelFormatter Functor to format the node label.
      * @param valueFormatter Functor to format the node value.
      */
-    void print(const std::string& s,
-               const LabelFormatter& labelFormatter = &DefaultFormatter,
-               const ValueFormatter& valueFormatter = &DefaultFormatter) const;
+    void print(const std::string& s, const LabelFormatter& labelFormatter,
+               const ValueFormatter& valueFormatter) const;
 
     // Testable
     bool equals(const DecisionTree& other,
@@ -266,20 +251,16 @@ namespace gtsam {
     }
 
     /** output to graphviz format, stream version */
-    void dot(std::ostream& os,
-             const LabelFormatter& labelFormatter = &DefaultFormatter,
-             const ValueFormatter& valueFormatter = &DefaultFormatter,
-             bool showZero = true) const;
+    void dot(std::ostream& os, const LabelFormatter& labelFormatter,
+             const ValueFormatter& valueFormatter, bool showZero = true) const;
 
     /** output to graphviz format, open a file */
-    void dot(const std::string& name,
-             const LabelFormatter& labelFormatter = &DefaultFormatter,
-             const ValueFormatter& valueFormatter = &DefaultFormatter,
-             bool showZero = true) const;
+    void dot(const std::string& name, const LabelFormatter& labelFormatter,
+             const ValueFormatter& valueFormatter, bool showZero = true) const;
 
     /** output to graphviz format string */
-    std::string dot(const LabelFormatter& labelFormatter = &DefaultFormatter,
-                    const ValueFormatter& valueFormatter = &DefaultFormatter,
+    std::string dot(const LabelFormatter& labelFormatter,
+                    const ValueFormatter& valueFormatter,
                     bool showZero = true) const;
 
     /// @name Advanced Interface