diff --git a/ompi/mca/coll/tuned/coll_tuned_decision_fixed.c b/ompi/mca/coll/tuned/coll_tuned_decision_fixed.c
index d1c36aeab8..3644eaba05 100644
--- a/ompi/mca/coll/tuned/coll_tuned_decision_fixed.c
+++ b/ompi/mca/coll/tuned/coll_tuned_decision_fixed.c
@@ -121,13 +121,13 @@ int ompi_coll_tuned_alltoall_intra_dec_fixed(void *sbuf, int scount,
     ompi_datatype_type_size(sdtype, &dsize);
     block_dsize = dsize * (ptrdiff_t)scount;
 
-    if ((block_dsize < ompi_coll_tuned_alltoall_small_msg)
+    if ((block_dsize < (size_t) ompi_coll_tuned_alltoall_small_msg)
                                               && (communicator_size > 12)) {
         return ompi_coll_tuned_alltoall_intra_bruck(sbuf, scount, sdtype, 
                                                     rbuf, rcount, rdtype,
                                                     comm, module);
 
-    } else if (block_dsize < ompi_coll_tuned_alltoall_intermediate_msg) {
+    } else if (block_dsize < (size_t) ompi_coll_tuned_alltoall_intermediate_msg) {
         return ompi_coll_tuned_alltoall_intra_basic_linear(sbuf, scount, sdtype, 
                                                            rbuf, rcount, rdtype, 
                                                            comm, module);