In summer 399, Lü Zuan and Lü Guang's heir apparent Lü Shao jointly attacked Northern Liang. Duan Ye sought aid from Southern Liang's prince Tufa Wugu, and Tufa Wugu sent his brother Tufa Lilugu and the general Yang Gui () to assist him. Duan Ye, because of the Southern Liang aid, was set to make a counterattack against Later Liang forces, but Juqu Mengxun persuaded him that doing so would give Southern Liang an opening to make a surprise attack, and so Duan Ye merely defended, and Lü Shao and Lü Zuan were forced to withdraw.