Birmingham have signed defender Paul Caddis from League One side Swindon for an undisclosed fee.
The full-back had a successful year-long loan at St Andrews last season, having found himself out of favour with then Swindon boss Paolo Di Canio.
The 25-year-old has agreed terms on a three-year deal.
Blues boss Lee Clark told bcfc.com: 'I'm delighted to bring Paul back to the club. He's obviously a player that we know very well and certainly not a gamble as he did the business for us last season.
"With Neal Eardley's situation it was important that we brought in another defender and, to add to that, Paul is a specialist right-back. When Neal returns we are going to have ourselves two very experienced right-backs."
Caddis, a former Celtic trainee, signed for Swindon in 2010 and captained the side to the League Two title in 2012.