diff --git a/test/datatype/checksum.c b/test/datatype/checksum.c
index ba55fc771e..98dafead1a 100644
--- a/test/datatype/checksum.c
+++ b/test/datatype/checksum.c
@@ -14,55 +14,94 @@
 #include "ompi/datatype/convertor.h"
 #include "ompi/datatype/datatype.h"
 
+#include <stdlib.h>
+
 #define SIZE 1024
 
+typedef struct {
+    int useful;
+    int useless;
+} my_data_t;
+
 int main( int argc, char* argv[] )
 {
     MPI_Datatype sparse;
-    int *array, *sparse_array, *packed;
+    int *array, *packed;
+    my_data_t* sparse_array;
     int i;
     uint32_t iov_count;
     size_t max_data, position;
     int32_t free_after;
-    uint32_t contiguous_checksum, sparse_checksum;
+    uint32_t pack_checksum, contiguous_checksum, sparse_checksum;
     struct iovec iov;
     ompi_convertor_t* convertor;
-    long extent;
 
     ompi_ddt_init();
+    srandomdev();
 
     ompi_ddt_create_vector( SIZE, 1, 2, MPI_INT, &sparse );
     ompi_ddt_commit( &sparse );
 
-    ompi_ddt_type_extent( sparse, &extent );
-
-    sparse_array = (int*)malloc( extent );
+    sparse_array = (my_data_t*)malloc( sizeof(my_data_t) * SIZE );
     array = (int*)malloc( sizeof(int) * SIZE );
     packed = (int*)malloc( sizeof(int) * SIZE );
     
-    for( i = 0; i < SIZE; packed[i] = i, i++ );
+    /**
+     * Initialize the sparse data using the index.
+     */
+    for( i = 0; i < SIZE; i++ ) {
+        sparse_array[i].useful = random();
+        sparse_array[i].useless = 0;
+    }
 
+    /**
+     * Pack the sparse data into the packed array. This simulate the first step
+     * of the buffered operation.
+     */
     convertor = ompi_convertor_create( ompi_mpi_local_arch, CONVERTOR_WITH_CHECKSUM );
     position = 0;
     ompi_convertor_personalize( convertor, CONVERTOR_WITH_CHECKSUM, &position, NULL, NULL );
-    ompi_convertor_prepare_for_recv( convertor, MPI_INT, SIZE, array );
+    ompi_convertor_prepare_for_send( convertor, sparse, SIZE, sparse_array );
 
     iov.iov_base = packed;
     iov.iov_len = sizeof(int) * SIZE;
     max_data = iov.iov_len;
 
     iov_count = 1;
-    ompi_convertor_unpack( convertor, &iov, &iov_count, &max_data, &free_after );
+    ompi_convertor_pack( convertor, &iov, &iov_count, &max_data, &free_after );
+    pack_checksum = convertor->checksum;
+
+    OBJ_RELEASE(convertor);
+
+    /**
+     * Now move the data from the packed array into the fragment to
+     * be sent over the network (still simulation).
+     */
+    convertor = ompi_convertor_create( ompi_mpi_local_arch, CONVERTOR_WITH_CHECKSUM );
+    position = 0;
+    ompi_convertor_personalize( convertor, CONVERTOR_WITH_CHECKSUM, &position, NULL, NULL );
+    ompi_convertor_prepare_for_send( convertor, MPI_INT, SIZE, packed );
+
+    iov.iov_base = array;
+    iov.iov_len = sizeof(int) * SIZE;
+    max_data = iov.iov_len;
+
+    iov_count = 1;
+    ompi_convertor_pack( convertor, &iov, &iov_count, &max_data, &free_after );
     contiguous_checksum = convertor->checksum;
 
     OBJ_RELEASE(convertor);
 
+    /**
+     * And now we're on the receiver side. We just get one fragment from
+     * the network and now we unpack it in the user memory.
+     */
     convertor = ompi_convertor_create( ompi_mpi_local_arch, 0 );
     position = 0;
     ompi_convertor_personalize( convertor, CONVERTOR_WITH_CHECKSUM, &position, NULL, NULL );
     ompi_convertor_prepare_for_recv( convertor, sparse, SIZE, sparse_array );
 
-    iov.iov_base = packed;
+    iov.iov_base = array;
     iov.iov_len = sizeof(int) * SIZE;
     max_data = iov.iov_len;
 
@@ -71,16 +110,24 @@ int main( int argc, char* argv[] )
     sparse_checksum = convertor->checksum;
 
     OBJ_RELEASE(convertor);
+
+    /**
+     * The datatype is not usefull anymore
+     */
     OBJ_RELEASE(sparse);
 
-    if( sparse_checksum != contiguous_checksum ) {
+    /**
+     * The 3 checksum have to match.
+     */
+    printf( "contiguous checksum %x\n", contiguous_checksum );
+    printf( "packed checksum     %x\n", pack_checksum );
+    printf( "sparse checksum     %x\n", sparse_checksum );
+    if( (sparse_checksum != contiguous_checksum) &&
+        (pack_checksum != sparse_checksum) ) {
         printf( "ERROR!!! the checksum algorithm does not work as expected\n" );
-        printf( "contiguous checksum %x != sparse checksum %x\n",
-                contiguous_checksum, sparse_checksum );
         return 1;
     }
-    printf( "contiguous checksum %x == sparse checksum %x\n",
-            contiguous_checksum, sparse_checksum );
+    printf( "COOL the 3 checksum match\n" );
 
     return 0;
 }