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Back-up to starter Alisson, Adrian joined the club as a free agent in 2019, making 24 appearances for the Reds.
The former West Ham keeper has won the Premier League, UEFA Super Cup and FIFA Club World Cup in his time at Anfield.
He played in six games in all competitions last season, keeping three clean sheets.
"I'm delighted, I'm very happy to stay in the club," Adrian said.
It is an honour for me to continue being a Red!!— Adrián San Miguel (@AdriSanMiguel) June 14, 2021
We will work hard to get & share with all of you some more great moments! Looking forward to see Anfield packed again!
¡Es un honor para mí continuar en el @LFC!
¡Trabajaremos duro para vivir grandes momentos juntos!
💪🏻🔴 #YNWA pic.twitter.com/OkSMvG9015
"Firstly, because it's a reward from the club for the hard work that I've been doing since I signed two years ago.
"I really appreciate that confidence from the club, from the manager and from everyone involved in that situation.
"And secondly, and above all of that, it's a pleasure to stay in Liverpool – it's such a big club. But being as well a family club, it's very special for any player to stay here. I am privileged."