Facebook’s stock dropped by up to 24 percent in after-hours trading on Wednesday after the company had reported slightly disappointing results for the second quarter and given out a growth warning for the upcoming quarters. The price drop temporarily wiped out almost $150 billion in market capitalization before the shares bounced back slightly later in the evening.

At first glance, Facebook’s results for the three months ending June 30 weren’t as catastrophic as the market reaction would suggest. The company reported a record profit of $5.1 billion on $13.2 billion in revenue, both roughly in line with Wall Street expectations. It was the financial outlook, given by David Wehner, the company’s CFO, that really caused Facebook’s share price to tumble. Wehner warned that operating margins would worsen over the next several years as expenses are anticipated to grow faster than revenue going forward. Moreover, he warned that revenue growth, an area where Facebook has excelled in recent years, would slow down significantly in the upcoming quarters.

One of the reasons for the expected slowdown is the rise of the Stories format, which isn’t as easily monetized as the News Feed, but there’s another area that could become cause for concern over the long run. Facebook’s user base has nearly stopped growing. While that isn’t a surprise given the social network’s size, the problem is that almost all its remaining growth is coming from regions where the company makes little money. As the following chart illustrates, Facebook added no daily active users in North America and Europe in the past quarter, which is unfortunate because every user in these regions brings in multiple times the revenue an active user in other parts of the world brings.