At the Consumer Electronics Show in Las Vegas last week, Netflix CEO Reed Hastings announced that the streaming-video provider is now in more than 160 countries worldwide, with more to come.

He also mentioned in passing that Netflix users watched 12 billion hours of programming in the last quarter of 2015, which is a huge number. At that rate, Netflix is averaging more than 4 billion hours of viewing per month, which makes it larger than almost any of the major TV networks except maybe CBS.

That’s massive growth, no matter how you look at it, which helped push the stock price NFLX up by more than 139% last year. But at least one research firm thinks that huge number could have a dark lining.

In a nutshell, Barclays Research said in a research note on Tuesday that the figure suggests Netflix’s subscriber base is growing more slowly than investors have been hoping, and that projections for the fourth quarter could be “at risk.” How did it come to that conclusion? By doing some reverse engineering.

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Netflix often talks about its growth, but Hastings’ speech is only the third time in the company’s history that it has mentioned total hours viewed, according to Barclays. So the firm took that figure and compared it to the total number of Netflix subscribers, to get the average number of hours a subscriber watches.

In the first quarter of last year, the average Netflix subscriber watched 161 hours of programming, Barclays says. If that number held steady for the fourth quarter, then it would mean that Netflix had about 74.7 million subscribers.

If that turns out to be the case, it won’t be the end of the world. Netflix wouldn’t miss its prior forecasts, and it wouldn’t miss the expectations of research firms like Barclays—but it would come awfully close. Barclays had projected 74.3 million subscribers, and the company itself has been guiding analysts to expect about the same.

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Barclays said, given the growth in Netflix’s programming over the past year, the number of hours viewed per subscriber should arguably have increased, not held steady. And if it did increase, then that could mean Netflix’s subscriber base has not grown as quickly as it led analysts to believe.

Even if it does turn out that Netflix meets estimates, the kind of investor who pays the type of multiple Netflix is trading at typically likes to see a company beat estimates handily, not barely manage to meet them. Whether Barclays is right or not will become obvious when the company reports its quarterly results on Jan. 19.