The energy-loss straggling of partially stripped ions of mass up to A = 35 has been measured in thin Al targets. The thickness uniformity of the Al targets was investigated by microbeam backscattering analysis, Talystep surface profiling, and electron microscopy to demonstrate that systematic errors arising from foil non-uniformity were negligible. The data for energy-loss straggling exceeded the Bethe-Livingston theoretical values by as much as a factor 2. This theory is however known to give reasonable estimates of the energy loss of light ions providing a suitable choice of the ion r.m.s. charge is used. We show that the fluctuation in charge states as the ions traverse the Al targets is an additional source of straggling that reconciles the Bethe-Livingston theory and observation in the case of nearly fully stripped 12C and 16O ions.