The speculative bonanza in special purpose acquisition companies, better known as Spacs, appears to be dead. Gary Gensler wants to make sure it doesn’t come back to life.

The Securities and Exchange Commission, which Gensler chairs, voted 3-2 on 24 January to adopt rules that seek to make it clearer to Spac investors if they are getting a raw bargain. Once the rules take effect in about five months, according to lawyers familiar with the deals, they will likely drive another nail into the coffin of a recent Wall Street fad fuelled by market froth and regulatory arbitrage.