Diagetic or Diegetic?

Just a little post to express my slight annoyance on how everyone spells the word diAgetic or diEgetic in different ways. I have seen in numerous texts it spelt with an 'a' and then in other ones an 'e'. I was undecided until I came across the word 'Diegesis' which is a word that is actually in the dictionary. So from that, even though I think it sounds better with an 'a', I'm going to spell it with an 'e', even though on some occasions I may spell it wrong.