diff --git a/json.h b/json.h
index fed608d..4b6a025 100644
--- a/json.h
+++ b/json.h
@@ -7,6 +7,7 @@
 #include <boost/fusion/include/define_struct.hpp>
 #include <boost/fusion/include/for_each.hpp>
 #include <boost/fusion/include/at.hpp>
+#include <boost/fusion/include/mpl.hpp>
 
 #include <json_spirit/json_spirit.h>