diff --git a/modules/io/src/mol/mmcif_writer.cc b/modules/io/src/mol/mmcif_writer.cc
index 4517ed943dbfa741a95702d886bec8dd0354b2ef..e14ff97d3d3c61ab4cb0513d17d24a83f98a56d4 100644
--- a/modules/io/src/mol/mmcif_writer.cc
+++ b/modules/io/src/mol/mmcif_writer.cc
@@ -1355,7 +1355,8 @@ namespace {
               }
             }
 
-            if(entity_infos[entity_idx].poly_type == "polyribonucleotide") {
+            if(entity_infos[entity_idx].poly_type == "polyribonucleotide" ||
+               entity_infos[entity_idx].poly_type == "polydeoxyribonucleotide/polyribonucleotide hybrid") {
               entity_infos[entity_idx].mon_ids[mon_id_idx] = "N"; 
               entity_infos[entity_idx].seq_olcs[mon_id_idx] = "N"; 
               entity_infos[entity_idx].seq_can_olcs[mon_id_idx] = "N";