Willis Tower might not be the most obvious place for a fast-growing Chicago tech startup to set up shop, but that’s exactly where BenchPrep is headed to keep up with the company’s increasing headcount.

BenchPrep, an e-learning startup that helps large education companies create online test prep tools for students, is moving into a new 15,000-square-foot space on the 57th floor of Willis Tower. The new office will more than double the startup’s square footage at its current office on South Jefferson Street. The company plans to move into the new space in December.

The move comes at a time of fast growth for the seven-year-old company. CEO Ashish Rangnekar declined to give specific revenue figures but said the company is profitable and cash-flow positive. BenchPrep will be at 40 employees by the end of 2017, up from 17 last year. And it plans to roughly double its current headcount by 2018, Rangnekar said. The startup has raised $8.2 million from well known investors like NEA, Revolution and Chicago’s Lightbank.

BenchPrep’s customers are large educational training companies like McGraw Hill, ACT, and CFA Institute. Those companies use BenchPrep’s technology to make tailored digital learning programs for their students to access on the web and mobile. Typically, customers sign multi-million dollar deals with BenchPrep for three to five years, Rangnekar said.

“We’re seeing a tremendous demand for our platform that enables industry leading companies to really transform their businesses and enter the new era of digital earning,” Rangnekar said. “I believe we are only beginning to scratch the surface of the opportunity here.”

BenchPrep’s move to Willis Tower comes as the Chicago landmark is undergoing a $500 million renovation, with plans to bring new restaurants, entertainment and retail space to its office tenants.

With tech companies flocking to River North and the West Loop, Rangnekar acknowledged that Willis Tower doesn’t exactly scream startup office. But being in the Chicago skyscraper brings some added credibility to the BenchPrep, whose old-school clients are likely to be more impressed by the Willis address than a trendy loft in Fulton Market.

“There’s some credibility being in the Willis Tower, which is arguably one of the most iconic buildings in the world,” Rangnekar said.