The Australian goalkeeper, 25, initially joined the O's at the beginning of February and will now remain with the League One club until the end of the season.
"I'm happy to have extended my stay and get a few more games under my belt," Cisak told Orient's official website.
"Unfortunately we didn't get the results in the last two games, but we need to get some more wins.
"We have got three big games coming up in a short space of time, starting with Yeovil on Saturday."
Since arriving at Brisbane Road, former Oldham Athletic gloveman Cisak has made seven appearances for Orient.
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