Brian Murphy has extended his Pompey contract until the end of the season.
The 32-year-old Irish goalkeeper has made 20 appearances since arriving at Fratton Park last summer.
His debut arrived in a 3-0 victory over Dagenham on the opening day of the campaign and he has kept 10 clean sheets in total.
Blues boss Paul Cook said: “We’re pleased to have agreed a new deal with Brian and he’s done a lot better than some people give him credit for.”
Murphy is likely to be in the side against former club Ipswich when Pompey visit Portman Road in the third round of the FA Cup on Saturday.