The iPhone 6S could be Apple's first flagship smartphone that fails to outdo its predecessor. In Apple Inc.’s report for the October-December quarter, KGI Securities analyst Ming-Chi Kuo forecasts iPhone sales to come in between 70 million and 75 million units, according to a research note obtained by MacRumors.

If his prediction is correct, Apple’s iPhone could either slightly edge out last year’s sales or fall into negative territory. Apple sold 74.5 million iPhones in its 2014 October-December quarter.

“[As] we do not expect overall demand for iPhone 6S to be significantly stronger than that for iPhone 6, we expect shipments momentum could gradually decline in [the quarter] on a year-on-year basis,” Kuo wrote in the note. “We expect iPhone may see its first year-on-year shipments decline in the first quarter of a year in 2016.”

His remarks echo a sentiment expressed by Bloomberg Intelligence’s senior equity analyst, John Butler, who wrote that the strength of the iPhone 6 sales cycle may prove “too difficult” for Apple to beat with the iPhone 6S. Apple and a number of other handset makers also face a weaker smartphone market, where shipments growth year over year is expected to slow to 10.4 percent, down from 27.4 percent in 2014, according to IDC.

Kuo also took his best guess for the Apple Watch, with an estimate of 3.5 million to 4 million units in the December quarter. But since Apple says it’s not releasing any specific sales data for the smartwatch, there isn’t much official data to compare it to.

Apple’s iPad may not see much of a turnaround in the period, with sales expected to fall between 14.5 and 15.5 million units shipped, down from 21.4 million iPads last year. But on the brighter side, Kuo expects Apple to sell 2 million units of the higher-priced iPad Pro in the December quarter, allowing it to offset some of the revenue decline in its tablet lineup.

Kuo also expects Mac sales to remain flat, between 5.4 million and 5.6 million units. Apple and Dell were the only companies to see any sales growth in the third quarter, according to Gartner.