diff --git a/minivhd.c b/minivhd.c
index 9f2a9f9..a56d1ec 100644
--- a/minivhd.c
+++ b/minivhd.c
@@ -565,34 +565,24 @@ int vhd_format_sectors(VHDMeta *vhdm, FILE *f, int offset, int nr_sectors)
 
         if (vhdm->type == VHD_DYNAMIC)
         {
-                int start_blk = offset / vhdm->sparse_spb;
-                int end_blk = (offset + (transfer_sectors - 1)) / vhdm->sparse_spb;
                 int sbsz = vhdm->sparse_sb_sz / VHD_SECTOR_SZ;
-                /* Most common case. No need to access multiple data blocks. */
-                if (start_blk == end_blk)
+                int prev_blk, curr_blk;
+                prev_blk = -1;
+                uint32_t s, ls, sib;
+                ls = offset + (transfer_sectors - 1);
+                for (s = offset; s <= ls; s++)
                 {
-                        uint32_t sib = offset % vhdm->sparse_spb;
-                        if (vhdm->sparse_bat_arr[start_blk] != VHD_SPARSE_BLK)
+                        curr_blk = s / vhdm->sparse_spb;
+                        if (vhdm->sparse_bat_arr[curr_blk] != VHD_SPARSE_BLK)
                         {
-                                uint32_t file_sect_offs = vhdm->sparse_bat_arr[start_blk] + sbsz + sib;
-                                fseeko64(f, (uint64_t)file_sect_offs * VHD_SECTOR_SZ, SEEK_SET);
-                                fwrite(zero_buffer, transfer_sectors * VHD_SECTOR_SZ, 1, f);
-                        }
-                }
-                else
-                {
-                        uint32_t s, ls;
-                        ls = offset + (transfer_sectors - 1);
-                        for (s = offset; s <= ls; s++)
-                        {
-                                int blk = s / vhdm->sparse_spb;
-                                uint32_t sib = s % vhdm->sparse_spb;
-                                if (vhdm->sparse_bat_arr[blk] != VHD_SPARSE_BLK)
+                                if (curr_blk != prev_blk)
                                 {
-                                        uint32_t file_sect_offs = vhdm->sparse_bat_arr[blk] + sbsz + sib;
+                                        sib = s % vhdm->sparse_spb;
+                                        uint32_t file_sect_offs = vhdm->sparse_bat_arr[curr_blk] + sbsz + sib;
                                         fseeko64(f, (uint64_t)file_sect_offs * VHD_SECTOR_SZ, SEEK_SET);
-                                        fwrite(zero_buffer, VHD_SECTOR_SZ, 1, f);
+                                        prev_blk = curr_blk;
                                 }
+                                fwrite(zero_buffer, VHD_SECTOR_SZ, 1, f);
                         }
                 }
         }