  We analyze the effects of finite-range corrections in halo effective field
theory for S-wave proton halo nuclei. We calculate the charge radius to
next-to-leading order and the astrophysical S-factor for low-energy proton
capture to fifth order in the low-energy expansion. As an application, we
confront our results with experimental data for the S-factor for proton capture
on Oxygen-16 into the excited $1/2^+$ state of Fluorine-17. Our low-energy
theory is characterized by a systematic low-energy expansion, which can be used
to quantify an energy-dependent model error to be utilized in data fitting.
Finally, we show that the existence of proton halos is suppressed by the need
for two fine tunings in the underlying theory.
