Arsenal manager Arsene Wenger said the Gunners fell short when they had to deal with the aerial threat of Andy Carroll - who scored a hatrick - in their 3-3 draw with West Ham on Saturday.
Arsenal threw away a two-goal lead before the England international scored three goals to make it 3-2, but Laurent Koscielny levelled the scoreline with 20 minutes from to go.
"He's good in the air. I believe we lost a bit of urgency. We had a good game today and we had a bad result and we paid for a weakness we've had throughout the season," Wenger said after the tie at Upton Park.
"If you look at the goals we've conceded since the start of the season, it's headers in our box and that happened today."
Wenger felt Carroll was lucky to remain on the pitch after his foul on Koscielny, but also said it wasn't an excuse for not sealing three points on the day.
"He's lucky to finish the game anyway," Wenger added. "But that doesn't mean we have to concede goals on the headers if he stays on the pitch, we have to look at ourselves and we cannot influence the decisions of the referee."