Portugal defender Ricardo Carvalho says his side must tighten up at the back after shipping four goals against Cyprus.
Carvalho, captaining the side in Cristiano Ronaldo's absence, saw Portugal share the spoils on Friday in an incredible 4-4 draw in Leiria.
The result came as a surprise with the Portuguese widely expected to finish winners of Group of H but they have the chance to recover against Norway on Tuesday.
And Carvalho has called on his colleagues to improve defensively after allowing the Cypriots to twice come back from 3-2 and 4-3 respectively to grab a point.
The Real Madrid defender told uefa.com ahead of the match in Oslo: "It's hard to say what happened (against Cyrpus)
"We didn't start well and Cyprus scored every time we made a mistake.
"We have to be more compact, especially at the back.
"We played well going forward but we're normally more secure in defence."
Norway head the group after opening up their campaign with a 2-1 win over Iceland, however manager Egil Olsen has warned his side they face a tough test against Portugal.
Olsen could be boosted by the return of striker John Carew after he missed the Iceland game with a knee injury as Norway search for their first win in nine attempts against Tuesday's opponents.
"I really hope we play better against Portugal than in the first half against Iceland," said the 68-year-old.
"The boys lifted themselves on Friday but we need an even better performance when we face the Portuguese."