Dixons Carphone has had to reissue its Christmas trading figures to say sales went down, not up over the period.
The retailer - which owns Currys PC World - had earlier reported a rise in sales, but later said it had made a "clerical error".
It issued a fresh statement for the last 10 weeks of the year, saying sales had fallen by 2% rather than risen by 2% as the firm had earlier reported.
Trading statements are not double checked by accountants.
Nonetheless, mistakes in official announcements are rare.
A rise in sales of supersize 65-inch TVs could not outpace a sharp fall in Dixons Carphone's struggling mobile phone business, where revenue fell 9%.
The fall in its phone arm is in line with expectations, and Dixons Carphone has said that it expects this to be a tough year for the mobile phone business.
Mobile sales have been under pressure because people are moving away from high-value monthly contracts and are upgrading their handsets less frequently.
The fall in sales follows a familiar trend.
Recent data from the British Retail Consortium revealed that retail sales fell for the first time in a quarter of a century last year.
And John Lewis recently warned that its staff bonus may be in doubt after reporting Christmas sales at its department stores dropped by 2%.
Dixons chief executive Alex Baldock hailed its Gaming Battlegrounds computer game experiences, which he said was helping gather more customers.
However, he told City analysts that he was "not counting" on an improvement in the UK shopping market.