We consider the case of a company that sells two substitutable varieties of the same product in a lead time-sensitive market. The regular product is manufactured and delivered with a make-to-order (MTO) system. The express product is delivered with a make-to-stock (MTS) system. The products (express and regular) are substitutable, so the demand of each product depends not only on his lead time but also on the lead time of the other product. We focus on the lead time decision of the MTO system (the other parameters are assumed to be known). We determine analytically the optimal solution and derive some insights.