diff --git a/src/App/PropertyExpressionEngine.h b/src/App/PropertyExpressionEngine.h
index 9a4982d2d2..b6ce8f9c08 100644
--- a/src/App/PropertyExpressionEngine.h
+++ b/src/App/PropertyExpressionEngine.h
@@ -177,7 +177,11 @@ private:
     typedef boost::adjacency_list< boost::listS, boost::vecS, boost::directedS > DiGraph;
     typedef std::pair<int, int> Edge;
     // Note: use std::map instead of unordered_map to keep the binding order stable
+    #ifdef FC_OS_MACOSX
+    typedef boost::unordered_map<const App::ObjectIdentifier, ExpressionInfo> ExpressionMap;
+    #else
     typedef std::map<const App::ObjectIdentifier, ExpressionInfo> ExpressionMap;
+    #endif
 
     std::vector<App::ObjectIdentifier> computeEvaluationOrder(ExecuteOption option);