diff --git a/src/base/ct2ctml.cpp b/src/base/ct2ctml.cpp
index e12974225..cb556c304 100644
--- a/src/base/ct2ctml.cpp
+++ b/src/base/ct2ctml.cpp
@@ -11,6 +11,7 @@
 
 #include <fstream>
 #include <sstream>
+#include <functional>
 
 #ifdef _WIN32
 #include <windows.h>