In 623, Feng, in addition to his other posts, also became acting minister of civil service matters. He was praised for his efficiency in the post. In 624, when Li Jiancheng was found to have improperly requisitioned soldiers to serve in his guard corps, and his guard commander Yang Wen'gan (楊文幹) then rebelled in fear, Emperor Gaozu considered deposing Li Jiancheng and replacing him with Li Shimin, but Feng made a secret submission arguing against such a move, and at least partly because of Feng's intercession, Emperor Gaozu did not depose Li Jiancheng. In 625, Feng was created the greater title of Duke of Dao, a title soon changed to Duke of Mi.