Index: common/tool/tool_manager.cpp
--- common/tool/tool_manager.cpp.orig
+++ common/tool/tool_manager.cpp
@@ -45,6 +45,8 @@
 
 #include <class_draw_panel_gal.h>
 
+#include <functional>
+
 /// Struct describing the current execution state of a TOOL
 struct TOOL_MANAGER::TOOL_STATE
 {
