Koscielny: Song return made Arsenal difference at Borussia Dortmund
Song returned to the squad after missing the last three games through suspension and Koscielny was pleased to see him back.
He said: "It's very important to have Alex [Song] near the centre-backs, because he stops the opportunities coming to the other team. It's good for us.
"We are in a good place now and we want to go and win at Blackburn."