Contrary to other replies, this is not remotely normal. Make sure you aren't misunderstanding the terms of your offer: some companies will say $x dollars worth of stock, with stock price determined by e.g. a 90-day running average. If there's a clause like that, and the stock went up so much since you joined (or signed the offer letter, depending on the terms) that the average price over the last 90 (or whatever) days is 2x higher than it was initially, then there's nothing shady going on.

If they didn't specify how they're determining a stock price to derive a # of shares from, or if they actually specified a number of shares rather than a dollar amount, then no, that's not normal. Get out and go somewhere else that doesn't play stupid games.