diff --git a/src/ComputingTasks.cc b/src/ComputingTasks.cc
index 0ed0c9fb..2da26b57 100644
--- a/src/ComputingTasks.cc
+++ b/src/ComputingTasks.cc
@@ -2269,7 +2269,7 @@ PlannerObjectiveStatement::checkPass(ModFileStructure &mod_file_struct, WarningC
   assert(model_tree.equation_number() == 1);
   if (model_tree.exoPresentInEqs())
     {
-      cerr << "ERROR: You cannot include exogenous variables in the planner objective. Please "
+      cerr << "ERROR: You cannot include exogenous variables (or variables of undeclared type) in the planner objective. Please "
            << "define an auxiliary endogenous variable like eps_aux=epsilon and use it instead "
            << "of the varexo." << endl;
       exit(EXIT_FAILURE);
diff --git a/src/ParsingDriver.cc b/src/ParsingDriver.cc
index 04e3541d..bf43e7fc 100644
--- a/src/ParsingDriver.cc
+++ b/src/ParsingDriver.cc
@@ -321,8 +321,9 @@ ParsingDriver::add_model_variable(const string &name)
     }
   catch (SymbolTable::UnknownSymbolNameException &e)
     {
-      // Declare variable as exogenous to continue parsing
-      // processing will end at end of model block if nostrict option was not passed
+      /* Declare variable as exogenous to continue parsing. Processing will end
+         at end of model block (or planner_objective statement) if nostrict
+         option was not passed. */
       declare_exogenous(name);
       undeclared_model_vars.insert(name);
       symb_id = mod_file->symbol_table.getID(name);
@@ -785,6 +786,7 @@ ParsingDriver::end_model()
           exit_after_write = true;
           cerr << it.second << endl;
         }
+  undeclared_model_variable_errors.clear();
 
   if (exit_after_write)
     exit(EXIT_FAILURE);
@@ -2022,6 +2024,21 @@ ParsingDriver::end_planner_objective(expr_t expr)
 
   mod_file->addStatement(make_unique<PlannerObjectiveStatement>(*planner_objective));
 
+  // Handle undeclared variables (see #81)
+  bool exit_after_write = false;
+  if (undeclared_model_variable_errors.size() > 0)
+    for (auto &it : undeclared_model_variable_errors)
+      if (nostrict)
+        warning(it.second);
+      else
+        {
+          exit_after_write = true;
+          cerr << it.second << endl;
+        }
+  undeclared_model_variable_errors.clear();
+  if (exit_after_write)
+    exit(EXIT_FAILURE);
+
   reset_data_tree();
 }