NSInteger to Int comparison in the block

Question

What mistake do I have below in the code could you please explain? I have button which has tag property that set 3 and interval also 3, which means 3 == 3 must be true but if is not working.

[_busyButtons enumerateObjectsUsingBlock:^(id  _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
    UIButton *button = (UIButton *)obj;
    int a = (int)button.tag;
    int b = (int)interval;
    if (a == b) {
        button.selected = YES;
    }

}];

details : ios9, xcode 7.0