diff --git a/types.hpp b/types.hpp
index e650d3c..46ce020 100644
--- a/types.hpp
+++ b/types.hpp
@@ -2,6 +2,7 @@
 
 #include <ifaddrs.h>
 
+#include <functional>
 #include <list>
 #include <string>
 #include <vector>