negative lookbefore for a blackslash in ruby 1.9

I want to match every '[' or ']' that's not preceded by a backslash in ruby 1.9 I tried:

/?&开发者_开发百科lt;!\134[\[\]]/

and

/?<!\\\\[\[\]]/

but I get a 'target of repeat operator not specified'

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You will need to wrap the negative lookbehind in parenthesis.

(?<!\\)[\[\]]