--- src/pingus/screens/demo_session.cpp.orig	2018-11-02 16:05:42 UTC
+++ src/pingus/screens/demo_session.cpp
@@ -17,6 +17,7 @@
 #include "pingus/screens/demo_session.hpp"
 
 #include <algorithm>
+#include <functional>
 #include <iostream>
 
 #include "engine/gui/gui_manager.hpp"