What is the issue with this Ruby code?

What is the issue with this Ruby code?

class Coordinate
  attr_reader :x, :y
  def initialize(x, y)
    @x, @y = x, y
  end
  def +(other)
    Coordinate.new(@x + other.x, @y + other.y)
  end
end
c1 = Coordinate.new(2, 3)
c2 = Coordinate.new(4, 5)
puts c1 + c2