Luton have re-signed Matthew Spring from Watford for an initial fee of £200,000 that could rise to £300,000.
Spring has not been a first-team regular this season
The 27-year-old left Luton for Leeds in 2004 and joined Watford the following year but has struggled to establish himself in the first team this season.
Spring has has signed a two-and-a-half year deal and Hornets boss Aidy Boothroyd said: "I think Matthew was brilliant for us.
"I'd like thank him for the part he played in helping secure promotion."
This season the Harlow-born player has been limited to just two Premiership starts and four substitute appearances, as well as turning out three times in cup competitions.