Java Thread Race Condition

Which statement best describes a potential concurrency issue in the following program?

public class Counter {
    private int count = 0;
    public void increment() { count++; }
    public int getCount() { return count; }
}

public class Worker extends Thread {
    private Counter counter;
    public Worker(Counter counter) { this.counter = counter; }
    public void run() {
        for (int i = 0; i < 1000; i++) {
            counter.increment();
        }
    }
}

public class Main {
    public static void main(String[] args) throws InterruptedException {
        Counter c = new Counter();
        Thread t1 = new Worker(c);
        Thread t2 = new Worker(c);
        t1.start();
        t2.start();
        t1.join();
        t2.join();
        System.out.println("Count is: " + c.getCount());
    }
}