Everton have conceded from corners in their last two matches.
The Toffees have conceded from corners in their last two outings – against Norwich City and Crystal Palace.
And, after Everton ended up drawing both of those matches, Martinez says that his side’s inability to defend from set pieces is costing them points.
"It is a problem at the moment," the Spanish boss said. "You shouldn’t concede from corners at that ratio. A corner cost us two points on Monday, and we conceded a corner and it cost us two points [against Norwich]."
Everton absolutely tore Norwich apart in the first half of their most recent contest, but they were made to pay for their profligacy.
The Merseyside outfit should have been out of sight at half time, but they only had a one-goal advantage and Norwich quickly turned the match around.
Wes Hoolahan poked home from a corner in the 47th minute, and Everton nearly lost all three points in the end.
The Canaries ended up missing some presentable chances to grab a winner, which would have kept them out of the relegation zone.
The draw continued Everton’s fine away record this term, but they are not winning regularly enough to break into the European qualification spots at the moment.