((xfs_bmbt_rec_base_t)blockcount &
                (xfs_bmbt_rec_base_t)XFS_MASK64LO(21));
 #else  /* !XFS_BIG_BLKNOS */
-       if (ISNULLSTARTBLOCK(b)) {
+       if (ISNULLSTARTBLOCK(startblock)) {
                r->l0 = ((xfs_bmbt_rec_base_t)extent_flag << 63) |
                        ((xfs_bmbt_rec_base_t)startoff << 9) |
                         (xfs_bmbt_rec_base_t)XFS_MASK64LO(9);
                 ((xfs_bmbt_rec_base_t)blockcount &
                  (xfs_bmbt_rec_base_t)XFS_MASK64LO(21)));
 #else  /* !XFS_BIG_BLKNOS */
-       if (ISNULLSTARTBLOCK(b)) {
+       if (ISNULLSTARTBLOCK(startblock)) {
                r->l0 = cpu_to_be64(
                        ((xfs_bmbt_rec_base_t)extent_flag << 63) |
                         ((xfs_bmbt_rec_base_t)startoff << 9) |