diff --git a/library/dhm.c b/library/dhm.c
index accd5a8..88e148b 100644
--- a/library/dhm.c
+++ b/library/dhm.c
@@ -231,8 +231,8 @@
         MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( ( X ),               \
                                                    p + 2,               \
                                                    ( n ) ) );           \
-        *p++ = (unsigned char)( ( n ) >> 8 );                           \
-        *p++ = (unsigned char)( ( n )      );                           \
+        *p++ = MBEDTLS_BYTE_1( n );                                     \
+        *p++ = MBEDTLS_BYTE_0( n );                                     \
         p += ( n );                                                     \
     } while( 0 )