We provide details of the error Gabor Ellmann found in 2004 in a heuristic argument of Guy and Kelly on this problem. This led to a correction of their conjectured upper bound for the no-three-in-line problem. However, details of the issue and its correction, including the actual location of the issue, while simple, do not seem to have appeared in the literature previously. That said, very recent work of Prellberg [5] does contain a derivation of the corrected conjectured upper bound.