Heroku koans: syntax error in triangle project 2?

about_triangle_project_2.rb

# http://koans.heroku.com/en/about_triangle_project_2
#
# XXX why does the second TriangleError.new cause a syntax error
# in the heroku web app, but not in my irb repl!?

class TriangleError < Exception
end

def triangle(a, b, c)
  sides = [a, b, c]

  # illegal side(s)?
  if sides.min <= 0
    raise TriangleError.new("a leg or two is of 0 or negative length")

  else
    _a, _b, h = sides.sort.map { |x| x*x }
    lw = _a + _b

    if lw < h || lw > h
      raise TriangleError.new("one or more legs is the wrong length")
    end
  end

  # OK, compute shape
  [:equilateral, :isosceles, :scalene].fetch(sides.uniq.size - 1)
end