diff --git a/src/DynareBison.yy b/src/DynareBison.yy
index 71de02c9eb0ac565ce97276980f1601de1a8de40..5dfad803206123585713ebaa841e23d31f5dbe7a 100644
--- a/src/DynareBison.yy
+++ b/src/DynareBison.yy
@@ -910,7 +910,9 @@ occbin_constraints_regime_options_list : occbin_constraints_regime_option
                                        | occbin_constraints_regime_options_list occbin_constraints_regime_option
                                          {
                                            $$ = $1;
-                                           $$.insert($2);
+                                           auto [it, success] = $$.insert($2);
+                                           if (!success)
+                                             driver.error("The '" + $2.first + "' clause is declared multiple times");
                                          }
                                        ;