The 24-year-old former Netherlands Under-15 keeper has made five senior appearances for the Championship club.
He had spells on loan with Rotherham and AFC Wimbledon last season, helping the Dons win promotion to League One.
"I was impressed with Kelle last season. He gives us added competition for the goalkeeping position," manager Darrell Clarke told the club website.
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League One club Bristol Rovers have signed Derby County goalkeeper Kelle Roos on a season-long loan deal.