SpaceX’s IPO is primed to be the biggest in history. Its bankers are worried about what comes next.

At a $2 trillion valuation, the listing could raise as much as $75 billion for Elon Musk’s rocket company. The problem is what happens months later, when early investors start selling, turn hundreds of billions of dollars of paper gains into cash, and create a wall of selling that drives the stock down. One idea that’s making the rounds among Wall Street banks: Let insiders sell some of that stock before the standard 180-day lock-up expires — but gradually, tied to price and potential trading volume thresholds.

The idea, which SpaceX may choose not to pursue, would be to ease more than $1 trillion worth of stock into the market over several months, rather than all at once, according to people familiar with the matter. In recent weeks, bankers have been canvassing potential investors for feedback, trying to strike a balance that ensures a smooth path for an IPO that Wall Street is counting on to go well, these people said.

SpaceX didn’t respond to requests for comment.