Dundee United manager Peter Houston admits his side must improve defensively after a second straight Scottish Premier League defeat.
"I felt that the Aberdeen players showed more desire to get their head on the ball," said Houston after losing 3-1 to the Dons at Pittodrie.
"If we are going to ship goals from set-plays then we have a major problem.
"There is no doubt that we aren't defending properly. That is something we will have to and work hard on."
Kari Arnason, Youl Mawene and Andrew Considine netted to give Aberdeen a 3-0 advantage and Lauri Dalla Valle pulled one back for the visitors late on.
"It was a disappointing second-half performance and there is no point lifting the ante when you are already 3-0 down," added Houston.