Defenders Ben Davies and Neil Taylor admit Wales need to address their set-piece vulnerability ahead of this summer's Euro 2016 finals.
Wales have conceded two set-piece goals in four days as Ukraine's winner in Kiev on Monday came from a free-kick.
The loss followed a draw with Northern Ireland when they scored from a corner.
"One loss of concentration from a set-piece has cost us. To concede from a set-piece is disappointing," said Tottenham Hotspur defender Davies.
"We have had plenty of meetings to sort it out. It was not the result we were looking for, but a lot about the performance was pretty good."
Fellow full-back Taylor was also not happy with Wales' potential Achilles heel as the Swansea defender added: "We didn't look troubled all night, but set-pieces were a problem."
Both Davies and Taylor, however, felt the positives outweighed the disappointment of defeat.
|Wales' Euro 2016 fixtures|
|11 June - Slovakia|
|16 June - England|
|20 June - Russia|
"It is not really about technical problems," said Davies. "It is about focus and concentration and not being able to switch off in these situations. We did tonight and it cost us."
Taylor agreed: "We are pleased with the performance, but not the goal we conceded. We've let ourselves down with that.
"We were in complete control of the game almost from start to finish, so we are disappointed not to score. Other than that, I thought we did very well.
"On another day we might have scored a couple. The way we conducted ourselves, we are happy with. But not the result."
Taylor feels plenty of the Wales fringe players have aided their bid to be part of Chris Coleman's 23-man squad that will head to France for their first European Championship finals.
"Quite a few players have staked their claims," he told BBC Radio Wales. "They are pushing for the Euro squad and no-one has done themselves any harm."