diff --git a/kernel/rtlil.cc b/kernel/rtlil.cc
index 0103cabfb..42d5f56b6 100644
--- a/kernel/rtlil.cc
+++ b/kernel/rtlil.cc
@@ -186,7 +186,7 @@ struct IdStringCollector {
 		trace(selection_var.selected_modules);
 		trace(selection_var.selected_members);
 	}
-	void trace_named(const RTLIL::NamedObject named) {
+	void trace_named(const RTLIL::NamedObject &named) {
 		trace_keys(named.attributes);
 		trace(named.name);
 	}