diff --git a/src/DynamicModel.cc b/src/DynamicModel.cc
index 1f8c99c2c2e2182071b2ab2166ecf23ad6214425..92fcc25326e3db2a87c18901c4030d215ff31456 100644
--- a/src/DynamicModel.cc
+++ b/src/DynamicModel.cc
@@ -4928,6 +4928,8 @@ DynamicModel::substituteDiff(StaticModel &static_model)
   for (int i = 0; i < (int) neweqs.size(); i++)
     addEquation(neweqs[i], -1);
 
+  copy(neweqs.begin(), neweqs.end(), back_inserter(aux_equations));
+
   if (diff_subst_table.size() > 0)
     cout << "Substitution of Diff operator: added " << neweqs.size() << " auxiliary variables and equations." << endl;
 }