One of the perks of Amazon's Prime membership is free two-day shipping on Prime-eligible purchases. That, however, might change. In a call to investors following Amazon's first quarterly earnings report today, CFO Brian Olsavsky said that the company is working on changing the two-day default to just one. Amazon already offers one-day Prime shipping on select orders, but two-day shipping is still the default. Olsavsky says that could change. "We're currently working on evolving our Prime shipping program, which has historically been a two-day program, to a one-day shipping program," he said. "We'll be building most of this capacity through the year in 2019." One of the ways Amazon hopes to do to this is by updating its infrastructure, building out fulfillment centers, and spending about $800 million to facilitate this change. Yahoo Finance reported that Amazon has shifted thousands of employees in an effort to increase fulfillment. The one-day shipping goal won't just be through Amazon's delivery service, but also through partners like UPS, FedEX and the US Postal Service. It's unclear if this will be a reality come this holiday season, but Olsavsky says that it is making "steady progress" towards this goal.