diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c b/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
index 126f93c0b0b89b5898853ab9329902a9cec9af3b..3914bfee0533b578a176a2de9de51ceb33a2ea82 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
@@ -1969,7 +1969,7 @@ static int vmw_surface_dirty_alloc(struct vmw_resource *res)
 		num_mip = 1;
 
 	num_subres = num_layers * num_mip;
-	dirty_size = sizeof(*dirty) + num_subres * sizeof(dirty->boxes[0]);
+	dirty_size = struct_size(dirty, boxes, num_subres);
 	acc_size = ttm_round_pot(dirty_size);
 	ret = ttm_mem_global_alloc(vmw_mem_glob(res->dev_priv),
 				   acc_size, &ctx);