In 866, at the time of the fire at the Otenmon Gate, TOMO no Yoshio, Dainagon (chief councilor of state) falsely accused MINAMOTO no Makoto (Kugyo) who held the position of Sadaijin (Minister of the Left), whereupon FUJIWARA no Yoshimi, who held the position of Udaijin (Minister of the Right) ordered Mototsune, who was Sakone no chujo, to arrest MINAMOTO no Makoto; however, Mototsune was suspicious of the charges, and notified his foster father Yoshifusa, whose efforts helped to prove MINAMOTO no Makoto's innocence.
貞観8年（866年）、応天門の炎上の際し大納言伴善男が左大臣源信(公卿)を誣告し、右大臣藤原良相が左近衛中将であった基経に逮捕を命じるも、基経はこれを怪しみ養父の良房に告げ、良房の尽力によって、源信は無実となった。