Index: head/sys/kern/vfs_vnops.c
===================================================================
--- head/sys/kern/vfs_vnops.c
+++ head/sys/kern/vfs_vnops.c
@@ -2167,7 +2167,8 @@
 		goto unlock;
 	}
 	bsize = vp->v_mount->mnt_stat.f_iosize;
-	for (bn = noff / bsize; noff < va.va_size; bn++, noff += bsize) {
+	for (bn = noff / bsize; noff < va.va_size; bn++, noff += bsize -
+	    noff % bsize) {
 		error = VOP_BMAP(vp, bn, NULL, &bnp, NULL, NULL);
 		if (error == EOPNOTSUPP) {
 			error = ENOTTY;