Yunjusi has, over the past few decades, earned a worldwide reputation for the immense repository of Buddhist scriptures carved on the stone slabs that are stored there (the so-called Stone Canon of Fangshan [Fangshan shijing]). The heroic enterprise of carving the whole Buddhist canon into stone had already been initiated during the Daye era (604–617) thanks to the resolve of the monk Jingwan (?–639) and support from Empress Xiao (d. after 630) of Sui Yangdi (r. 604–617) and her brother Xiao Yu (574–647). However, it did not accelerate until 740 when Xuanzong, as urged by his sister Princess Jinxian (689–732), ordered two eminent monks from the capital monastery Great Chongfusi (one of them being the great Buddhist historian and cataloguer Zhisheng [fl. 740s]) to deliver over four-thousand fascicles of Buddhist translations, which constituted the main body of the newly compiled Kaiyuan Buddhist canon, to Yunjusi to serve as base texts for the stone scriptures. This event is remarkable and puzzling for at least three reasons. First, although Yunjusi, a local temple situated far from the capitals, was not a Kaiyuan monastery, it still had the honour of being chosen as a recipient of the Kaiyuan canon. Second, one cannot help but wonder why and how two Chongfusi monks, who were of obvious prestige, should have demonstrated such enthusiasm in escorting so many Buddhist texts to this apparently marginal temple. Finally, it is difficult to understand why Princess Jinxian, who was then an ordained Taoist nun, played such an active and decisive role in this project. Such a remarkable and important event inevitably invited considerable attention from scholars, who have noted, and attempted to explain, several aspects of the mystery surrounding Princess Jinxian's Yunjusi ties. This article attempts to address this old issue from a perspective that has never been explored. It broaches and elaborates on the possibility that the great AvatamD saka master Fazang's (643–712) possible ties with Yunjusi form a major missing piece in this complex puzzle.