A major post-crisis rule taking effect in December will force Blackstone and other creators of complex securities to eat some of their own cooking. Many of them are already engineering ways to keep it to a nibble.

Starting Christmas Eve, the 2010 Dodd-Frank regulatory overhaul will require companies that package most types of loans into bonds to keep at least 5% of the securities they create. The intent is to prevent a repeat of crisis-era behaviour, in which loan quality fell dramatically as lenders passed all of the risk along to investors.