Fashion sales at John Lewis fell by 2% for the week to 28 July.
The fall came on the back of a 3.5% drop in the middle of the month for the week to 14 July, as the hot weather dulled footfall. Total sales across the department store fell by 2.2%.
Warm-weather clothing, however, continued to sell well as a result of the consistent high temperatures, and sales of summer ranges were up 29% on 2017.
Menswear sales also rose by 2.1%.