Problem in simple loop

Hi, all!
I'm using Twine 2.1.3 and SugarCube 2.18.0.

This doesn't work:

<<set _outcome to 0>>
<<for _outcome == 0>>
	Loop
	<<if _outcome == 1>>
		$victory
		<<goto $victory>>
	<</if>>
	<<set _outcome to 1>>
	_outcome
<</for>>

Apparently, _outcome is set to 1 at the end of the first iteration, but the condition "_outcome == 1" is not recognized. Ridiculous syntax problem, of course, but where ?

Thanks in advance.