diff --git a/mecab/src/dictionary.h b/mecab/src/dictionary.h
index 7046023..32ad358 100644
--- a/mecab/src/dictionary.h
+++ b/mecab/src/dictionary.h
@@ -10,6 +10,7 @@
 #include "mmap.h"
 #include "darts.h"
 #include "char_property.h"
+#include <functional>
 
 namespace MeCab {