diff --git a/play_motion2/include/play_motion2/motion_loader.hpp b/play_motion2/include/play_motion2/motion_loader.hpp
index 35210fd..0d4ba88 100644
--- a/play_motion2/include/play_motion2/motion_loader.hpp
+++ b/play_motion2/include/play_motion2/motion_loader.hpp
@@ -16,6 +16,7 @@
 #define PLAY_MOTION2__MOTION_LOADER_HPP_
 
 #include <string>
+#include <functional>
 
 #include "play_motion2/types.hpp"