diff --git a/include/orz/mem/pot.h b/include/orz/mem/pot.h
index 4b08c97..86a42b1 100644
--- a/include/orz/mem/pot.h
+++ b/include/orz/mem/pot.h
@@ -7,6 +7,7 @@
 
 #include <mutex>
 #include <memory>
+#include <functional>
 
 namespace orz {