diff --git a/inference/Key.h b/inference/Key.h
index dfd7f3574..1c957486d 100644
--- a/inference/Key.h
+++ b/inference/Key.h
@@ -12,6 +12,7 @@
 #include <iostream>
 #include <boost/format.hpp>
 #include <boost/serialization/serialization.hpp>
+#include <boost/serialization/nvp.hpp>
 #ifdef GTSAM_MAGIC_KEY
 #include <boost/lexical_cast.hpp>
 #endif