Does breaking the fast of someone observing a supererogatory fast necessitate only making up the missed day without expiation?

Whoever breaks a voluntary fast must make it up (qada'), due to the hadith of Aisha (may Allah be pleased with her): "Hafsah and I were fasting, and some food was presented to us which we desired, so we ate from it. He [the Prophet] said: 'Make up for it by fasting another day in its place.'" The command to make up the fast implies obligation.