The penultimate stage from Modane to Valfrejus will remain at 110.5km and still finish at the top of the 21 hairpins of l'Alpe d'Huez but the ascent of the Galibier will be replaced by a punishing climb to the Col de la Croix de Fer which has an average gradient of 5.2 per cent.
The peloton will leave Modane as scheduled, then will head north after traversing Saint-Michel-de-Maurienne.
The riders will climb the col de la Croix de Fer pass a second time, but attacked from a different slope than the day before on stage 19.
They then descend into the Oisans Valley to re-join the original route, before beginning the climb to Alpe d’Huez.
As a result of this course change, the Henri Desgrange prize, which rewards the rider who leads at the highest point of the Tour, will be awarded at the col d’Allos (2250 metres), just prior to the finish of stage 17 at Pra-Loup.
The Tour de France is scheduled to start on 4 July in Utrecht, Netherlands.