diff --git a/src/isoburn.c b/src/isoburn.c
index 3ce59312..b0619a46 100644
--- a/src/isoburn.c
+++ b/src/isoburn.c
@@ -239,12 +239,6 @@ int isoburn_prepare_disc_aux(struct burn_drive *d, struct burn_disc **disc,
  if(ret<0)
    return -1;
  
- // TODO check return values for failure. propertly clean-up on error
- 
- *disc = burn_disc_create();
- session = burn_session_create();
- burn_disc_add_session(*disc, session, BURN_POS_END);
- 
  wopts.volnum = 0;
  wopts.level = opts->level;
  wopts.flags = opts->flags;
@@ -264,11 +258,25 @@ int isoburn_prepare_disc_aux(struct burn_drive *d, struct burn_disc **disc,
  wopts.input_charset = opts->input_charset;
  wopts.ouput_charset = opts->ouput_charset;
  
- wopts.ms_block = (new_img ? 0 : o->nwa);
+ if (new_img) {
+   wopts.ms_block = 0;
+ } else {
+   int lba, nwa;
+   ret = isoburn_disc_track_lba_nwa(d, NULL, 0, &lba, &nwa);
+   if (ret != 1)
+     return -2;
+   wopts.ms_block = nwa;
+ }
+
  wopts.src = o->src;
  wopts.overwrite = (new_img ? NULL : o->target_iso_head);
  wsrc = iso_source_new_ecma119(o->target_volset, &wopts);
-
+ 
+ // TODO check return values for failure. propertly clean-up on error
+ 
+ *disc = burn_disc_create();
+ session = burn_session_create();
+ burn_disc_add_session(*disc, session, BURN_POS_END);
  track = burn_track_create();
  burn_track_set_source(track, wsrc);
  burn_session_add_track(session, track, BURN_POS_END);