diff --git a/libisofs/libisofs.h b/libisofs/libisofs.h
index 5865771..b7aac0a 100644
--- a/libisofs/libisofs.h
+++ b/libisofs/libisofs.h
@@ -3488,7 +3488,11 @@ int el_torito_seems_boot_info_table(ElToritoBootImage *bootimg, int flag);
  *                   iso_write_opts_set_hfsplus().
  *                   @since 1.2.4
  *                Primary GPT and backup GPT get written if at least one 
- *                ElToritoBootImage shall be mentioned
+ *                ElToritoBootImage shall be mentioned.
+ *                The first three mentioned GPT partitions get mirrored in the
+ *                the partition table of the isohybrid MBR. They get type 0xfe.
+ *                Often it is one of these MBR partitions which actually gets
+ *                used by EFI.
  *                @since 1.2.4
  *        bit8= Mention in isohybrid Apple partition map
  *              APM get written if at least one ElToritoBootImage shall be
diff --git a/libisofs/system_area.c b/libisofs/system_area.c
index 26ccf94..12644c2 100644
--- a/libisofs/system_area.c
+++ b/libisofs/system_area.c
@@ -1578,7 +1578,7 @@ int iso_write_system_area(Ecma119Image *t, uint8_t *buf)
         img_blocks = t->curblock;                  /* value might be altered */
         ret = iso_offset_partition_start(img_blocks, t->partition_offset,
                                          t->partition_secs_per_head,
-                                         t->partition_heads_per_cyl, buf, 1);
+                                         t->partition_heads_per_cyl, buf, 0);
         if (ret != ISO_SUCCESS) /* error should never happen */
             return ISO_ASSERT_FAILURE;
     }