New Zealand fast bowler Lockie Ferguson will be available for Derbyshire for the remainder of the 2018 season.
The 27-year-old joined the county in June on a contract for their T20 Blast fixtures, but can now play in the County Championship as well.
South Africa paceman Duanne Olivier played for the county in the first half of the season, and is their leading Championship wicket-taker with 31.
"It's a chance for me to develop my game," Ferguson told the club website.
"It's a great opportunity and it's also another challenge to play for a team where you're expected to turn up and take wickets."
Ferguson has taken 124 first-class wickets but has only played at international level in limited-overs formats.