Index: src/Common/utility.h
===================================================================
--- src/Common/utility.h	(revision 447c35601995880f86baa595fb0755c65564b620)
+++ src/Common/utility.h	(revision 2e30d4738767687bb4971a4daa4a83789c031a4c)
@@ -18,4 +18,5 @@
 #include <cctype>
 #include <algorithm>
+#include <functional>
 #include <iostream>
 #include <iterator>