PHOENIX — A top credit ratings firm is boosting its rating on Arizona State University’s debt, citing the university’s ongoing growth in enrollment, student charges and financial reserves.

Moody’s Investors Service announced Tuesday that it upgraded ASU’s debt one notch to its third highest rating of Aa2. Higher ratings can translate into lower borrowing costs. The rating affects $1.2 billion of outstanding system revenue bonds and an upcoming $154 million bond sale.

Moody’s also upgraded ASU’s three other types of debt one notch to Aa3, its fourth highest rating.

Both project a stable outlook for university debt. The ratings firm also noted that ASU’s growing brand recognition has led to growing and sustained donor support, rising net tuition and improved research activity.