Can't Queue with a player less than a full tier below me

I've played two ranked solo/duo queues with a friend of mine. We are both in provisional ranks, for the first game he was completely unranked and I was provisional Silver 1. Then he became Bronze 2 and we play another. I then hit Gold 4 and he hit Silver 2. Now the game won't let us play together... Any reason why/solution to it?