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The Netherlands goalkeeper's previous deal was set to run out in June 2016, but the 25-year-old has agreed fresh terms until 2018.
And Cillessen is thrilled to be extending his stay at the Amsterdam Arena.
"Once again, this is a contract that exudes trust," he told the club's official website. "A contract extension with Ajax remains special.
Article continues below"18 months ago, everything was different. That shows how fast things can move. A lot has happened in the last year."
Cillessen moved to Ajax from NEC in August 2011 for a reported €3 million fee and he has gone on to make 69 appearances for the first team.
"This sends a good signal," he said. "Jasper, along with Davy Klaassen, Joel Veltman and Ricardo van Rhijn, among others, have bound themselves to the club for a longer period of time.
"If the current group remains together for a minimum of two years great things will happen."
