diff --git a/sys/fs/msdosfs/msdosfs_fat.c b/sys/fs/msdosfs/msdosfs_fat.c
index c2cff2378e54..9cb7634019ff 100644
--- a/sys/fs/msdosfs/msdosfs_fat.c
+++ b/sys/fs/msdosfs/msdosfs_fat.c
@@ -321,8 +321,8 @@ updatefats(pmp, bp, fatbn)
 	struct buf *bp;
 	u_long fatbn;
 {
-	int i;
 	struct buf *bpn;
+	int cleanfat, i;
 
 #ifdef MSDOSFS_DEBUG
 	printf("updatefats(pmp %p, bp %p, fatbn %lu)\n", pmp, bp, fatbn);
@@ -362,12 +362,23 @@ updatefats(pmp, bp, fatbn)
 		 * filesystem was mounted.  If synch is asked for then use
 		 * bwrite()'s and really slow things down.
 		 */
+		if (fatbn != pmp->pm_fatblk || FAT12(pmp))
+			cleanfat = 0;
+		else if (FAT16(pmp))
+			cleanfat = 16;
+		else
+			cleanfat = 32;
 		for (i = 1; i < pmp->pm_FATs; i++) {
 			fatbn += pmp->pm_FATsecs;
 			/* getblk() never fails */
 			bpn = getblk(pmp->pm_devvp, fatbn, bp->b_bcount,
 			    0, 0, 0);
 			bcopy(bp->b_data, bpn->b_data, bp->b_bcount);
+			/* Force the clean bit on in the other copies. */
+			if (cleanfat == 16)
+				((u_int8_t *)bpn->b_data)[3] |= 0x80;
+			else if (cleanfat == 32)
+				((u_int8_t *)bpn->b_data)[7] |= 0x08;
 			if (pmp->pm_flags & MSDOSFSMNT_WAITONFAT)
 				bwrite(bpn);
 			else