Component state not updating after unchecking checkbox in React

I simply want to change the state of my app with a handleChange method for multiple checkboxes.

My state is changed from false to true when I click each of my checkboxes, but when I un-check it, my state doesn't change to reflect it and I cant seem to figure out why!

import React, { Component } from "react";

export class StepOne extends Component {
    constructor(props) {
        super(props);
        this.state = {
            box1: false,
            box2: false,
            box3: false,
        };
    }

    handleChange = (evt) => {
        const box = evt.target.name;
        this.setState({ [box]: !this.state.box });
    };

    render() {
        return (
            <div>
                <input type="checkbox" name="box1" onChange={this.handleChange} />
                <input type="checkbox" name="box2" onChange={this.handleChange} />
                <input type="checkbox" name="box3" onChange={this.handleChange} />
            </div>
        );
    }
}