diff --git a/demo-cxx/demo.cc b/demo-cxx/demo.cc
index b975e88..04287b8 100644
--- a/demo-cxx/demo.cc
+++ b/demo-cxx/demo.cc
@@ -10,7 +10,7 @@
 ThingC::~ThingC() { std::cout << "done with ThingC" << std::endl; }
 
 std::unique_ptr<ThingC> make_demo(rust::Str appname) {
-  return std::unique_ptr<ThingC>(new ThingC(appname));
+  return std::unique_ptr<ThingC>(new ThingC(std::string(appname)));
 }
 
 const std::string &get_name(const ThingC &thing) { return thing.appname; }