diff --git a/sys/fs/msdosfs/msdosfs_fat.c b/sys/fs/msdosfs/msdosfs_fat.c
index 32da0e3eedb9..7fae9c0ec100 100644
--- a/sys/fs/msdosfs/msdosfs_fat.c
+++ b/sys/fs/msdosfs/msdosfs_fat.c
@@ -1065,13 +1065,13 @@ extendfile(dep, count, bpp, ncp, flags)
 					    pmp->pm_bpcluster, 0, 0, 0);
 				else {
 					bp = getblk(DETOV(dep),
-					    de_cn2bn(pmp, frcn++),
+					    frcn++,
 					    pmp->pm_bpcluster, 0, 0, 0);
 					/*
 					 * Do the bmap now, as in msdosfs_write
 					 */
 					if (pcbmap(dep,
-					    de_bn2cn(pmp, bp->b_lblkno),
+					    bp->b_lblkno,
 					    &blkno, 0, 0))
 						bp->b_blkno = -1;
 					if (bp->b_blkno == -1)