diff --git a/simgear/nasal/cppbind/NasalHash.hxx b/simgear/nasal/cppbind/NasalHash.hxx
index 54efc2c5194f9c6fa8c52a528aff56228c576d90..1734adf682e0614671675c5dad2f9dfd5d91838d 100644
--- a/simgear/nasal/cppbind/NasalHash.hxx
+++ b/simgear/nasal/cppbind/NasalHash.hxx
@@ -5,6 +5,8 @@
 #ifndef SG_NASAL_HASH_HXX_
 #define SG_NASAL_HASH_HXX_
 
+#include <boost/mpl/if.hpp>
+
 #include "from_nasal.hxx"
 #include "to_nasal.hxx"