diff --git a/drivers/xen/gnttab.c b/drivers/xen/gnttab.c
index 2308cfaf8b1448..aea46f0ad2e4e5 100644
--- a/drivers/xen/gnttab.c
+++ b/drivers/xen/gnttab.c
@@ -343,12 +343,12 @@ static int gnttab_init(void)
 		put_free_entry(gref);
 	}
 
-	for (i = 0; i < NR_GRANT_FRAMES; i++) {
+	for (i = NR_GRANT_FRAMES; i; i--) {
 		xatp.domid = DOMID_SELF;
 		xatp.size = 0;
 		xatp.space = XENMAPSPACE_grant_table;
-		xatp.idx = i;
-		xatp.gpfn = xen_virt_to_gfn(Z_TOPLEVEL_ROM_NAME(grant_tables).phys_addr) + i;
+		xatp.idx = i - 1;
+		xatp.gpfn = xen_virt_to_gfn(Z_TOPLEVEL_ROM_NAME(grant_tables).phys_addr) + (i - 1);
 		rc = HYPERVISOR_memory_op(XENMEM_add_to_physmap, &xatp);
 		__ASSERT(!rc, "add_to_physmap failed; status = %d\n", rc);
 	}