Russian diamond miner Alrosa joined rival De Beers in cutting prices for its gems, but with a twist — the company changed its billing system so buyers can’t tell which stones are discounted, or by how much.

The two biggest producers for months refused to cut prices even as sales collapsed during the coronavirus pandemic, to avoid giving up too much ground before demand returned. De Beers and Alrosa don’t publish prices for their rough stones and their dominance in the often-secretive diamond industry has allowed the two companies to dictate terms to their customers over the years.

In a sign the miners see demand returning, De Beers cut prices by almost 10% for larger stones earlier this week. Alrosa’s buyers also lowered prices in the most recent sale, according to people familiar with the situation. However, instead of the usual individually priced diamond parcels, the company issued a single invoice total for each customer, the people said. Alrosa didn’t explain the change, they said.