Facebook Inc (NASDAQ:FB) investors have been partying for some time. Year-to-date, FB stock is up more than 30%. Over the last three years, it has more than doubled. Over the last 5 years? The stock has seen a near 400% gain.

After a rough IPO, it really has been a tremendous run for Facebook stock. And if Credit Suisse’s recent 2018 forecast — a 45% jump from Friday’s close of $151.44 — is any indication, sentiment regarding the stock’s future seems to be positive.

But the run has taken somewhat of a pause recently. Since early May, shares have hovered right around $150. It isn’t unusual for a stock that has run up so much to consolidate at a certain level, but this is a noticeably long period of share price stagnation for FB stock.

Investors shouldn’t be worried.

Facebook stock has some problems it will face in 2017 with slowing growth and rising expenses. But those problems have easy fixes.

Here’s why I remain a buyer of FB stock.

Facebook Stock and the Ad Load Problem

Advertisements aren’t cool, but they make money. Social media platforms like Facebook aim to strike a critical balance between how much money they make and how many ads they throw on their site.

The market terminology for the number of ads a social media player can put on their site is “ad load”. According to management in the July 2016 earnings call, the mainstay Facebook app is nearing max ad load. The topic dominated the call. Ad load was again a big discussion point in the November 2016 earnings call as management said ad revenue growth would slow meaningfully in 2017. The reason why? Higher ad load would be less of a growth driver going forward.

That same bearish outlook was reiterated in the February 2017 and May 2017 calls.

That is a big deal, because ad revenue was $7.9 billion last quarter. Total revenue was $8 billion. So when FB management says ad revenue growth is supposed to slow meaningfully, they are essentially saying total revenue growth is supposed to slow meaningfully.

That is an even bigger deal because expense growth is picking up. Revenues grew 54% last year. Total expenses grew 30%. That led to significant operating leverage and earnings growth of 171% for Facebook stock.

But this year revenue growth will be meaningfully less than 54%. Analysts see it at roughly 40%. But total expenses are expected to grow somewhere between 40% and 50% next year. That implies operating margin compression. It is also why analysts only see something like 15% earnings growth next year for Facebook.

At 25.5-times next year’s consensus earnings estimate, FB needs to do a little more than 15% earnings growth to justify that valuation.

The good news for investors is that Facebook may just be getting started in terms of global growth.

WhatsApp Fixes Facebook’s Ad Load Problem

Naturally, FB investors are focused on the Facebook, Instagram and Messenger growth stories. After all, those are the big apps in the United States. Moreover, Facebook and Instagram are the only ones generating any meaningful revenue.

But the often forgotten WhatsApp, which FB purchased for $19 billion in early 2014, may be the company’s most compelling growth component. WhatsApp has 1.2 billion monthly active users, as large as Messenger. But most of those users are abroad. The app also doesn’t make any money yet. Naturally, U.S. and revenue-focused investors lose sight of the WhatsApp growth story.

But what happens when Facebook monetizes those 1.2 billion users?

Mark Meeker’s annual internet trends report shows just how popular WhatsApp is abroad. With over 200 million users in India, WhatsApp has become the most popular Android app in India. The mainstay Facebook app is the fifth most popular.

But the report shows that WhatsApp is more than just popular. It’s also valuable. Brands are already using WhatsApp to promote themselves. For example, digital health start-up 1mg exploded in popularity because of a message one of the company’s users posted on WhatsApp. The message, which praised 1mg’s services, got shared over and over and over … and that eventually led to 9 million downloads of 1mg’s app.

In other words, international brands are already realizing the value of WhatsApp as an advertising platform. To me, that means that WhatsApp will start making money fairly soon.

So lets play with some numbers.

At a meager $2 in average revenue per user (ARPU), WhatsApp could generate $2.4 billion per quarter. If global advertisers recognize WhatsApp as an advertising platform with as much value as Facebook, then WhatsApp could be looking at global ARPU potential of $4 (around Facebook’s current ARPU). In that scenario, WhatsApp could generate $4.8 billion per quarter.

Overall, when FB starts monetizing WhatsApp, that will add somewhere between $10 and $20 billion in ad revenue per year. Facebook generated just under $28 billion in revenue last year. So we are talking about an incremental 35% to 70% boost to the topline.

That’s huge, and could be what fixes Facebook’s slowing ad revenue growth problem. If WhatsApp starts generating money, Facebook won’t need ad load to be a growth driver to sustain strong overall revenue growth.

Bottom Line on FB Stock

WhatsApp will one day make a lot of money for Facebook. When that happens, FB stock will rocket higher.

Right now looks like a good entry point considering the recent flattish price action.

As of this writing, Luke Lango was long FB.