Rule reference is not currently supported in a set in ANTLR4 Grammar

Rule reference is not currently supported in a set in ANTLR4 Grammar

I am trying to port Chris Lambro's ANTLR3 Javascript Grammar to ANTLR4
I am getting the following error,
Rule reference 'LT' is not currently supported in a set
in the following code
LineComment
    : '//'  ~(LT)* -> skip
    ;

LT      : '\n'      // Line feed.
    | '\r'      // Carriage return.
    | '\u2028'  // Line separator.
    | '\u2029'  // Paragraph separator.
    ;
I need help understanding why I am getting this error, and how I can solve it .