The 23-year-old agreed a six-year deal following his arrival at the Vicente Calderon from Benfica in 2014.
The Slovenian has since gone on to make almost 50 appearances for Atletico, who have now rewarded him with a one-year extension.
During his 29 appearances in all competitions this season, Oblak has kept 18 clean sheets.
By Taiwo Oyedeji
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