  We show that order-parameter fluctuations in a good type-I superconductor or
a liquid crystal always increase the size of the first-order transition. This
behavior is eventually changed when the system crosses over to inverted-XY
critical behavior, with the size of the first-order transition vanishing as a
power law with a crossover exponent. We find a good agreement between our
theory and a recent experiment on the nematic-smectic-A first-order transition
in 8CB-10CB mixtures of liquid crystals.
