diff --git a/preprocessor/ExprNode.cc b/preprocessor/ExprNode.cc
index fcf19ec51..5620b11a2 100644
--- a/preprocessor/ExprNode.cc
+++ b/preprocessor/ExprNode.cc
@@ -5140,6 +5140,17 @@ FirstDerivExternalFunctionNode::compileExternalFunctionOutput(ostream &CompileCo
     }
 }
 
+expr_t
+FirstDerivExternalFunctionNode::cloneDynamic(DataTree &dynamic_datatree) const
+{
+  vector<expr_t> dynamic_arguments;
+  for (vector<expr_t>::const_iterator it = arguments.begin();
+       it != arguments.end(); it++)
+    dynamic_arguments.push_back((*it)->cloneDynamic(dynamic_datatree));
+  return dynamic_datatree.AddFirstDerivExternalFunctionNode(symb_id, dynamic_arguments,
+                                                            inputIndex);
+}
+
 SecondDerivExternalFunctionNode::SecondDerivExternalFunctionNode(DataTree &datatree_arg,
                                                                  int top_level_symb_id_arg,
                                                                  const vector<expr_t> &arguments_arg,
@@ -5336,3 +5347,14 @@ SecondDerivExternalFunctionNode::writeExternalFunctionOutput(ostream &output, Ex
       output << ");" << endl;
     }
 }
+
+expr_t
+SecondDerivExternalFunctionNode::cloneDynamic(DataTree &dynamic_datatree) const
+{
+  vector<expr_t> dynamic_arguments;
+  for (vector<expr_t>::const_iterator it = arguments.begin();
+       it != arguments.end(); it++)
+    dynamic_arguments.push_back((*it)->cloneDynamic(dynamic_datatree));
+  return dynamic_datatree.AddSecondDerivExternalFunctionNode(symb_id, dynamic_arguments,
+                                                             inputIndex1, inputIndex2);
+}
diff --git a/preprocessor/ExprNode.hh b/preprocessor/ExprNode.hh
index c77c8cbcf..c0de01b82 100644
--- a/preprocessor/ExprNode.hh
+++ b/preprocessor/ExprNode.hh
@@ -874,6 +874,7 @@ public:
                                              bool lhs_rhs, const temporary_terms_t &temporary_terms,
                                              const map_idx_t &map_idx, bool dynamic, bool steady_dynamic,
                                              deriv_node_temp_terms_t &tef_terms) const;
+  virtual expr_t cloneDynamic(DataTree &dynamic_datatree) const;
 };
 
 class SecondDerivExternalFunctionNode : public ExternalFunctionNode
@@ -899,6 +900,7 @@ public:
   virtual void writeExternalFunctionOutput(ostream &output, ExprNodeOutputType output_type,
                                            const temporary_terms_t &temporary_terms,
                                            deriv_node_temp_terms_t &tef_terms) const;
+  virtual expr_t cloneDynamic(DataTree &dynamic_datatree) const;
 };
 
 #endif