diff --git a/grub-core/loader/i386/pc/chainloader.c b/grub-core/loader/i386/pc/chainloader.c
index c79c4fe0f..18220b7aa 100644
--- a/grub-core/loader/i386/pc/chainloader.c
+++ b/grub-core/loader/i386/pc/chainloader.c
@@ -117,7 +117,7 @@ grub_chainloader_patch_bpb (void *bs, grub_device_t dev, grub_uint8_t dl)
 
       if (bpb->num_reserved_sectors == 0)
 	break;
-      if (bpb->num_total_sectors_16 == 0 || bpb->num_total_sectors_32 == 0)
+      if (bpb->num_total_sectors_16 == 0 && bpb->num_total_sectors_32 == 0)
 	break;
 
       if (bpb->num_fats == 0)
diff --git a/include/grub/fat.h b/include/grub/fat.h
index 4a5aab793..8d7e4a1e5 100644
--- a/include/grub/fat.h
+++ b/include/grub/fat.h
@@ -28,20 +28,15 @@ struct grub_fat_bpb
   grub_uint16_t bytes_per_sector;
   grub_uint8_t sectors_per_cluster;
   grub_uint16_t num_reserved_sectors;
-  grub_uint8_t num_fats;
-  /* 0x10 */
+  grub_uint8_t num_fats;		/* 0x10 */
   grub_uint16_t num_root_entries;
   grub_uint16_t num_total_sectors_16;
-  grub_uint8_t media;
-  /*0 x15 */
+  grub_uint8_t media;			/* 0x15 */
   grub_uint16_t sectors_per_fat_16;
-  grub_uint16_t sectors_per_track;
-  /*0 x19 */
-  grub_uint16_t num_heads;
-  /*0 x1b */
-  grub_uint32_t num_hidden_sectors;
-  /* 0x1f */
-  grub_uint32_t num_total_sectors_32;
+  grub_uint16_t sectors_per_track;	/* 0x18 */
+  grub_uint16_t num_heads;		/* 0x1A */
+  grub_uint32_t num_hidden_sectors;	/* 0x1C */
+  grub_uint32_t num_total_sectors_32;	/* 0x20 */
   union
   {
     struct