Can I substitute granulated sugar for caster sugar in Marzipan?

I’d like to make marzipan, but I don’t have caster/superfine sugar, only "regular" white sugar. Will it work, or are there any tricks to make it work without a grinding implement?

---

I just finished a batch after using a blender to grind up the sugar (the almond was already in powder form). The consistency might be a bit coarser, but I’m not sure I can tell the difference.