Uncaught ReferenceError: 'constructor' is not defined

So I'm creating some modules for my project, one of them being a class. This class is in the Modules folder, and is being require'd in. Here's the opening code snippet:

class Potentiometer {
	constructor(config, PID) {
		this.config = config;
		this.PID = PID;
		this.registeredCallbackTimerId = undefined;
		this.setValueTimerId = undefined;
		this.currentValue = 0;
	}
...
}

exports = Potentiometer;

...and of course I'm doing this in the main code:

let Potentiometer = require('potentiometer');
let pot = new Potentiometer(config, PID);

When I run the code, I get the 'constructor' is not defined error. I'm on fw 1.93 if that matters. I could use a little help.