The experienced defender, who joined Rovers on a season long loan deal from Bolton Wanderers last Friday, can operate anywhere across the back four.
The Rovers boss just missed out on signing the 28-year-old last season, but is pleased to have secured his services this time around.
"We're delighted to get him," said the Rovers boss. "He was someone that when we first took over we were probably just a little bit late to get in.
"We've monitored him and kept our eye on him and we are thankful to Dougie Freedman to allow us to get it done.
"It has been no secret in terms of where we felt we've needed to strengthen and in Alex we've gained more than just one player, he can play anywhere across the back four."
Baptiste has travelled with the rest of the first team squad for a week of warm weather training in Portugal. Rovers are next in pre-season action on Wednesday 23rd July when they take on Accrington Stanley at the Store First Stadium, kick-off 7.45pm.
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