diff --git a/src/duality/duality_wrapper.cpp b/src/duality/duality_wrapper.cpp
index 08c5d1f8a..705d71abe 100644
--- a/src/duality/duality_wrapper.cpp
+++ b/src/duality/duality_wrapper.cpp
@@ -606,7 +606,7 @@ expr context::make_quant(decl_kind op, const std::vector<sort> &_sorts, const st
   void model::show_hash() const {
     std::ostringstream ss;
     model_smt2_pp(ss, m(), *m_model, 0);
-    std::hash<std::string> hasher;
+    stl_ext::hash<std::string> hasher;
     unsigned h = hasher(ss.str());
     std::cout << "model hash: " << h << "\n";
   }