convert: non-conforming drawing primitive definition

Why do I get:

convert: non-conforming drawing primitive definition `circle 15,15 15,1' @ error/draw.c/DrawImage/3143.

When executing this ImageMagick code?

var fs = require('fs');
var spawn = require('child_process').spawn;

var bg = function (size) {

  var args = ['-size', '30x30', 'xc:none', '-fill', '-', '-draw', '"circle 15,15 15,1"', '-'];
  var convert = spawn('convert', args);
  convert.stderr.on('data', function (data) { console.log(data.toString()); });
  convert.stdin.pipe = convert.stdout.pipe.bind(convert.stdout);
  return convert.stdin;

};

module.exports = bg;