--- src/pingus/screens/demo_session.cpp.orig	2018-01-15 12:30:12.557430067 +0100
+++ src/pingus/screens/demo_session.cpp	2018-01-15 12:30:24.416546179 +0100
@@ -16,6 +16,7 @@
 
 #include "pingus/screens/demo_session.hpp"
 
+#include <functional>
 #include <algorithm>
 #include <iostream>
 
