Apple's primary assembly partner, Foxconn, said on Thursday that it saw revenues for the month of December drop 8.3 percent year-over-year, likely a reflection of weak iPhone demand.

Revenues slid to $20.12 billion versus $21.91 billion in 2017, Reuters reported. It's the first such decline since last February.

"The main reason is that the fall for consumer category products was rather big," a Foxconn representative said, without providing detail on which clients or products were the culprits.

Foxconn is heavily dependent on Apple orders, and the iPhone in turn is Apple's biggest product. Manufacturing is usually most intense in late summer and the fall as the two companies prepare to launch new models then cope with holiday demand.

Apple CEO Tim Cook confessed to soft iPhone sales earlier this month, pointing his finger mostly at the Chinese market. He put lesser blame on other markets, as well as factors like "foreign exchange headwinds," fewer carrier subsidies, and even discounted battery replacements, which some have called an admission that Apple depends on degraded batteries to spur upgrades.

In a recent interview Cook denied suggestions that the iPhone XR has been a flop, saying it has been the bestselling iPhone model since its launch. That may simply be bad news, however, for the iPhone XS and XS Max.