Index: include/tool/tool_interactive.h
--- include/tool/tool_interactive.h.orig
+++ include/tool/tool_interactive.h
@@ -32,6 +32,8 @@
 #include <tool/tool_event.h>    // Needed for CONTEXT_MENU_TRIGGER
 #include <tool/tool_base.h>
 
+#include <functional>
+
 class ACTION_MENU;
 
 
