Small-angle neutron scattering measurements on an Al-7.5 wt.% Cr-1 wt.% Fe alloy, grown by vapour deposition, have revealed a sequence of changes in cluster shape during low-temperature precipitate growth. The interpretation arose from a Monte Carlo model which allowed the shape of particular clusters to be followed as a function of time and temperature, and compared with the corresponding scattering pattern. An evolution in cluster shape from predominantly linear, through planar, to roughly spherical was found, depending on the coordination number of cluster atoms stable at each temperature.