Replaying a Single Frame

This question seems very elementary, and I’m surprised that after using Flash for a few years, I’ve never come across an ideal solution. I’ve come up with several satisfactory ways to work around the issue, but never a direct solution. Anyway…the question - How can I replay a single frame until some condition is met? For example (I realize this is not practical and could be handled with a for loop, but just for the sake of simplicity):

Frame 20
if (c == 1000){
trace(“i’m done”);
gotoAndPlay(20); // <-- I realize this doesn’t work, but it’s the idea I want

How can I accomplish this without adding an extra movie clip or using 2 frames? Thanks.