Joby Aviation stock declined 8.8% in after-hours trading Tuesday following the company’s announcement of plans to offer $500 million of common stock.

The air taxi developer said it would offer shares with an aggregate price of $500 million and intends to grant underwriters a 30-day option to purchase up to an additional $75 million of common stock at the offering price, less underwriting discounts and commissions.

The significant share offering appears to have triggered investor concerns about potential dilution of existing stockholders, leading to the sharp decline in Joby’s stock price after the regular trading session ended.

Joby Aviation is developing electric vertical takeoff and landing aircraft (eVTOL) for commercial passenger service, with plans to launch air taxi operations in the coming years. The company will likely use the proceeds from this offering to fund ongoing development and certification efforts for its aircraft.