How to avoid an user can delete a sales order or a purchase order ?

Hello,

I'd want to prevent an user to delete an invoiced order (sales or purchase order). How to do ?

For the sales order, I found a parameter "delete orders" in the permissions (Security / Sales Ledger / Periodic), and I set "no access" but the user can anyway remove an order.

I didn't find any parameter for the purchase orders.

Thanks in advance for your help,

regards,

Eric