NTT Docomo will replace about 930,000 SIM cards due to manufacturing errors, the company said Tuesday.

The recall involves about 510,000 NTT Docomo SIM cards and some 420,000 from other carriers using the Docomo network. The cards might become unusable even if they are functioning normally now, the company said.

Cards with the defect were manufactured between December 2021 and October 2022. They have serial numbers that start with GD06, according to NTT Docomo.

The company said it will notify affected users by mail from mid-October, and that card replacement will be free of charge. Users are not required to return the old cards by mail.

“We deeply apologize for the inconvenience and concern this has caused our customers,” NTT Docomo said.