diff --git a/src/muz/duality/duality_dl_interface.cpp b/src/muz/duality/duality_dl_interface.cpp
index aa186bd0a..9227059aa 100755
--- a/src/muz/duality/duality_dl_interface.cpp
+++ b/src/muz/duality/duality_dl_interface.cpp
@@ -327,10 +327,10 @@ lbool dl_interface::query(::expr * query) {
   try {
     ans = rs->Solve();
   }
-  catch (Duality::solver::cancel_exception &exn){
+  catch (const Duality::solver::cancel_exception &){
     throw default_exception("duality canceled");
   }
-  catch (Duality::Solver::Incompleteness &exn){
+  catch (const Duality::Solver::Incompleteness &){
     throw default_exception("incompleteness");
   }