The Hoops are left in just two competitions as they lead the league by 15 points and await the cup semi-final with Dundee United next month but goalkeeper Forster wants to ensure there is no complacency as they chase a double.
"We want to wrap the league up as quickly as possible so we're all 100% focused on the job," Forster told this week's Celtic View.
"We can't be complacent, though. We have to go out and keep trying – a lot hasn't changed in the league, we still have to go out and perform well.
"A few times we've had a gap at the top of the table and it hasn't meant we've dipped in form so hopefully that doesn't start happening now.
"We all want to win the Scottish Cup, especially after the disappointment of losing the League Cup semi-final, so it's vital we get to the final this time.
"It's important we're fully focused because we know it will be a tough game against Dundee United when it comes around. We're going for the double so we're still very motivated."