Real Madrid captain Sergio Ramos has said his side have learned from a major dip in form two years ago and will not allow it to happen again.
Madrid went 22 games without defeat under Carlo Ancelotti in 2014, winning the World Club Cup, but lost to Valencia in La Liga and Atletico Madrid after the winter break and ended the season without another trophy.
They are currently on a 33-game unbeaten run and, with home games against Borussia Dortmund and Deportivo La Coruna to come, could set a new club record of 35 by the time they fly to Japan for this year's World Club Cup next week.
But speaking to the club's official website ahead of the Champions League game against Dortmund, Ramos warned: "Not many years ago, we had a very similar run without losing and then things got complicated after Christmas.
"It is very fresh in the memory. We had major drop in form. Mistakes are there to learn from, and hopefully it will be a wake-up call so it does not happen again."
Defender Jesus Vallejo, impressing on loan from Madrid at Eintracht Frankfurt this season, told AS how he thought his parent club could beat Dortmund.
Frankfurt recently defeated them in the Bundesliga, and Vallejo said stopping Julian Weigl initiating moves from deep was the best way to thwart Thomas Tuchel's team.
"Weigl is, for me, the key to everything," Vallejo said. "He drops back between the centre-backs to start moves, and everything starts there.
"If you can stop him doing that, Dortmund find things much more difficult. When he is not comfortable, their dangerous players in attack do not receive clear passes."
Vallejo said Madrid would need to defend as a team against the threat of attackers Pierre-Emerick Aubameyang and Ousmane Dembele.
"I have found out personally how difficult it is to mark Aubemayang," he said. "Sometimes it seems he is not in the game, hardly involved in the play, and suddenly he makes a run which cuts right through you.
"I was especially impressed with Dembele. It is incredible how he uses both feet and hardly loses any speed as he carries the ball, so it is crucial that the full-back gets help from the defensive midfielder or centre-halves."