diff --git a/usr.sbin/makefs/msdos/msdosfs_vnops.c b/usr.sbin/makefs/msdos/msdosfs_vnops.c
--- a/usr.sbin/makefs/msdos/msdosfs_vnops.c
+++ b/usr.sbin/makefs/msdos/msdosfs_vnops.c
@@ -500,6 +500,7 @@
 		cpsize = MIN((nsize - offs), blsize - on);
 		memcpy(bp->b_data + on, dat + offs, cpsize);
 		bwrite(bp);
+		brelse(bp);
 		offs += cpsize;
 	}