Negative times with Sytem.nanoTime()

I'm not sure why this is happening, every time when I get to 10 in the timer the numbers start going negative. Heres the code:

@Test
void testTimeSortCompator() {
    System.out.println("Time to find largest sort comparator:");
    for (int i = 0; i < inputArraySizes.length; i++) {
        int total = 0;
        for (int j = 0; j < numRunsToAverage; j++) {
            list = (List<Integer>) createList(inputArraySizes[i]);
            total += doSortComparator();
        }   
        System.out.println(inputArraySizes[i] + " " + (total / numRunsToAverage));
    }
}



private long doSortComparator() {
    int temp = (int) Math.floor((Math.random() * (100 - 1) + 1));
    long start = System.nanoTime();
    FindKLargest.findKLargestSort(list, temp, intComparator);
    long stop = System.nanoTime();
    long duration = (stop - start);
    return duration;
    
}

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