diff --git a/src/ModelTree.cc b/src/ModelTree.cc
index 5d89e7b2e9c7d25113ca695ab76d0ca2176c3bc4..952d0c05b181c73a7cfe2a0008b1e7eaef41d26b 100644
--- a/src/ModelTree.cc
+++ b/src/ModelTree.cc
@@ -124,6 +124,9 @@ ModelTree::ModelTree(SymbolTable &symbol_table_arg,
   NNZDerivatives(4, 0),
   temporary_terms_derivatives(4)
 {
+  // Ensure that elements accessed by {Static,Dynamic}Model:write{Json,}ParamsDerivativesFile() exist
+  for (const auto &ord : {pair{0, 1}, pair{1, 1}, pair{0, 2}, pair{1, 2}, pair{2, 1}, pair{3, 1}})
+    params_derivatives.emplace(ord, decltype(params_derivatives)::mapped_type{});
 }
 
 ModelTree::ModelTree(const ModelTree &m) :