Pompey have been scoring plenty of goals recently, with 12 notched in the past four League One fixtures.
But Kenny Jackett is now keen to see some more stingy performances at the opposite end of the pitch.
His side are heading for Accrington this weekend, looking to increase their 10-match unbeaten run in all competitions.
And with the gap between them and the play-off places just three points, Jackett wants Pompey to keep raising the bar.
The Blues boss said: “We haven’t been as tight or efficient at the back as we’d like in recent games and there have been a few too many goals conceded.
“So it’s important we don’t let that continue. We won’t be able to keep pace with the sides at the top of the table if we don’t improve in that area.
"We certainly have the players who can form a back four that will help us go on the sort of run we’re looking for."
“We’ll obviously have to make changes with Brandon Haunstrup requiring an operation and Christian Burgess suspended for one game.
“But we certainly have the players who can form a back four that will help us go on the sort of run we’re looking for.
“We need to find the right combination to keep some more clean sheets and serve the forward players.
“Accrington is a hard place to visit. They’ll take the game to you and we have to match them, making sure our attitude and approach is spot on.”
There was sad news earlier in the week with the death of popular former Pompey manager Jim Smith.
Jackett said: “He’s not someone I knew very well, but he had a fantastic career over many years and with a lot of clubs.
“From everything I’ve been told, he was also a great character and it’s a sad loss for football in general.”