diff --git a/src/ParsingDriver.cc b/src/ParsingDriver.cc
index fafa902228ee9aa1e9806a1f23e77ab9489f2c08..9f14c410483b0f4284ee9460d12f2675838b0272 100644
--- a/src/ParsingDriver.cc
+++ b/src/ParsingDriver.cc
@@ -2636,6 +2636,7 @@ ParsingDriver::pac_model()
   if (it == options_list.string_options.end())
     error("You must pass the discount option to the pac_model statement.");
   auto discount = it->second;
+  check_symbol_is_parameter(discount);
 
   mod_file->addStatement(make_unique<PacModelStatement>(name, aux_model_name, discount,
                                                         pac_growth,