The 21-year-old had been on trial with the League One side after leaving Heerenveen, for whom he failed to play a league match in two seasons there.
Sietsma spent time on loan at Dutch second-tier side FC Emmen last term.
"This is a big club in a big stadium and I'm looking forward to the season," he told the club website.
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MK Dons have signed Dutch goalkeeper Wieger Sietsma on a free transfer on a two-year deal with the option of a further year.