Startup accidentally gave me 2 option grants instead of 1, can I keep both?

I joined a startup and in my contract they state that I will receive X number of stock options, I received a grant for that amount which I accepted. A couple months later, I received another grant for that amount, which I also accepted. It looks like the company caught on and are trying to rectify the situation by having me sign something and somehow return the second grant. Do I have to do return the options or can I keep them because they gave me 2 grants