Does fraud require deliberate deception?

Some libertarians, most notably Walter Block, have tried to argue that fraud does not require deliberate deception. For example, argues Block, if I tried to sell you a square circle, and I believed that square circles existed, and so did you, and you agreed to the transaction, then, since square circles do not actually exist, this would still count as fraud, even though no deliberate deception has taken place. Block has used this argument to indict fractional reserve banking, by arguing that it still counts as fraud even though all parties are knowingly consenting. Is he talking rationalist nonsense?