Verizon has signed an agreement to acquire fiber optic internet provider Frontier in a deal valued at $20 billion. In its press release announcing the transaction, Verizon says the deal “will significantly expand Verizon’s fiber optic coverage across the country and accelerate the delivery of premium mobility and broadband services to existing and new customers.”

The deal with Frontier could help Verizon win back its legacy Fios subscribers after Frontier bought some of its wireline assets — including Fios’ fiber-optic internet connections — for $10.5 billion in 2015. Frontier’s existing 2.2 million fiber-optic subscribers in 25 states will now join Verizon’s roughly 7.4 million Fios connections in nine states. Frontier currently has 7.2 million fiber-optic sites and plans to add another 2.8 million by the end of 2026.

“The acquisition of Frontier is a strategic decision,” said Hans Vestberg, Verizon’s chairman and CEO. “It builds on Verizon’s two decades of fiber optic leadership and is an opportunity to become more competitive in more markets across the United States, enhancing our ability to deliver premium offerings to millions more customers over a combined fiber optic network.”