We can move to the south pole from any longitude.

lib/map.rb

@@ -61,7 +61,7 @@ def next_location_backwards(location:)
   end
 
   def located_at_north_pole?(coordinates)
-    coordinates == Coordinates.new(x: 0, y: 9)
+    @x_domain.map { |x| Coordinates.new(x: x, y: 9) }.include?(coordinates)
   end
 
   private

lib/mars_rover.rb

@@ -15,7 +15,7 @@ def execute(commands)
         when 'f'
           new_location = forwards(location)
           if @map.located_at_north_pole? new_location.coordinates
-            Location.new(coordinates: Coordinates.new(x: 0 + 18, y: 8), direction: 'S')
+            Location.new(coordinates: Coordinates.new(x: new_location.coordinates.x + 18, y: 8), direction: 'S')
           else
             new_location
           end

spec/moving_forwards_spec.rb

@@ -139,6 +139,14 @@ def self.mars_rover(map: Map.new(x_domain: (0..10), y_domain: (0..10)), located_
       expect(mars_rover).to be_facing('S')
     end
 
+    it 'can move to the north pole from any longitude' do
+      mars_rover = a_mars_rover(located_at: Location.new(coordinates: Coordinates.new(x: 1, y: 8), direction: 'N'))
+
+      mars_rover.execute(['f'])
+
+      expect(mars_rover).to be_located_at(Coordinates.new(x: 19, y: 8))
+    end
+
     it 'can move to the south pole of the planet'
 
     it 'faces north upon reaching the south pole'