diff --git a/include/boost/mpi/detail/mpi_datatype_cache.hpp b/include/boost/mpi/detail/mpi_datatype_cache.hpp
index cc073e2..c99ddb1 100644
--- a/include/boost/mpi/detail/mpi_datatype_cache.hpp
+++ b/include/boost/mpi/detail/mpi_datatype_cache.hpp
@@ -88,7 +88,7 @@ private:
 };
 
 /// Retrieve the MPI datatype cache
-mpi_datatype_map& mpi_datatype_cache();
+BOOST_MPI_DECL mpi_datatype_map& mpi_datatype_cache();
 
 } } } // end namespace boost::mpi::detail