Mixing single- and dual-rank RAM usually works fine.

Probably not. The rank (single vs. dual) is less important than matching speed, timings, and voltage. If your existing stick is single-rank and you add a dual-rank stick of the same speed and timings, it will almost certainly work.

The real gotcha is that dual-rank sticks are slightly harder on the memory controller. On older motherboards or with four sticks, that can force the system to drop to a lower speed (like 3200 instead of 3600). But for a simple two-stick setup on a modern board? You likely won’t notice a difference.

If you can match the exact same model, do that. If not, don’t lose sleep over rank. Speed and CAS latency matter way more.

Just run MemTest86 after installation to be sure.