Score doesn't work

I have this when the scores should be increasing:
[AS]_root.score +=4;[/AS]
It works the first time and goes from 0 to 4, but any time after that it just adds fours. So in the end it ends up saying “4444444444” or something. I tried it this way also:
[AS]_root.score = _root.score+4;[/AS]
But that didn’t work either. It just did the same thing. Help please! :frowning: