Responses to 4NT ace-asking:

5C  no ace
5D  ace of clubs
5H  ace of diamonds
5S  ace of hearts
5NT ace of spades
6C  two aces of the same colour
6D  two aces of the same rank
6H  two non-touching aces (S+D or H+C)
7C  three aces

The advantage of this is that we can now open 4NT on hands such as:

S AKQJT98
H KQJT
D -
C KQ

or

S KQJ
H KQJT9876
D AK
C -

ie. looking for two specific aces. This works whenever the long suit is a major,
unless the long suit is hearts and the void is in spades.