Gary Caldwell says he is surprised that Celtic have built a seven-point lead over Rangers at the top of the league.
But despite the gap Caldwell is wary of a revival to match the champions' title comeback last season when they trailed Rangers by the same margin in April.
"Rangers dropping points has obviously surprised us because they are a great side," said the Celtic defender.
"We're in a position where we are ahead and we have to maintain that; we found out last year that it's never over."
Celtic went on to claim their third successive Scottish Premier League title after reeling in their Glasgow rivals in the final months of last season.
The Parkhead club have won all 12 league games since losing 4-2 at home to Rangers back in August.
"We have obviously been on a great run; to win 12 games in any league is a great achievement," Caldwell continued.
"Rangers showed in the first Old Firm game that they are a top team. They have made a few mistakes and we have been lucky enough to punish them for it."
Caldwell does not expect Rangers to repeat their weekend defeat to Hearts very often, and he knows they are capable of going on a similar run to Celtic's.
Walter Smith's side won 13 SPL games in a row last season, another fact which backs up Caldwell's caution.
"If you are as good as they are, in this league you are going to have to have a run where you win a lot of games; we have to be ready for that," the versatile Scotland defender said.
Celtic will bid for their 13th win in a row when Caldwell faces his former club, Hibernian, at Easter Road on Sunday.
MY SPORT: DEBATEThe winning run is a great source of pride to the 26-year-old, especially as Celtic have faced a series of injuries to key players such as Aiden McGeady and Jan Vennegoor of Hesselink.
"We have worked really hard," Caldwell said. "We have had injuries in the run that we have had.
"I think everyone who has been involved is very proud of it.
"It's not finished yet, we want to keep it going and see how many we can win on the bounce. It's a great achievement to win 12 and we want more."
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