The cornerstone of Apple’s eye-watering profits remains the iPhone. While Apple’s other business divisions are growing at speed, the unbelievable profit margins that Apple rakes in on the iPhone make the company what it is.

So any threat to Fortress iPhone is a big deal for Apple. One-off problems, like manufacturing slowdowns or battery scandals, can be excused just as long as people keep lusting after the latest and greatest iPhone. But if that allure ever goes away, Apple is in trouble, which makes a new survey from Cowen unfortunate reading for Apple execs.

Cowen, a Wall Street research firm that gathers data from investors, frequently runs a study asking people what kind of phone they’re going to buy next. It’s a simple measure of brand loyalty and desirability, and unfortunately, Cowen found that the number of current iPhone owners planning to buy a new iPhone “was near the lowest levels since conducting our survey.”

Now, that doesn’t mean that Apple fans are jumping ship wholesale. 80.5% of current iPhone owners still plan on upgrading to a new iPhone next time around, which is still the kind of loyalty that other companies crave. But with virtually everyone in the developed world already owning a smartphone, Apple’s future profits depend heavily on current iPhone owners remaining loyal, as well as getting some Android buyers to defect. So, the fact that iPhone owners’ loyalty has dropped from 87.6% last quarter down to 80.5% this quarter is bad news.

“iPhone appeal moderating across the industry,” Cowen wrote in the report, seen by Fierce Wireless. “When asked ‘what kind of cell phone do you think you will get with your next upgrade/purchase,’ the percent of postpaid respondents at AT&T, Sprint and Verizon selecting iPhone moderated vs. last quarter while at the same time just 80.5% of postpaid respondents who already have an iPhone indicated they will get one with their next upgrade/purchase, which was near the lowest levels since conducting our survey and was down from 87.6% last quarter.”

Speculation is running rampant about how successful the iPhone X has been in its first three months on sale. The first quarterly earnings after a new iPhone release are always a big deal, and a strong indicator of how successful a phone will be overall. But limited iPhone X supply at launch means that sales are going to have to remain strong through most of 2018 in order for the iPhone X to be a real success. That means converting everyone who’s thinking about buying a new phone, not just the early adopters and avid Apple lovers who are going to buy a new iPhone, no matter what.