COVID-19 test kit maker Ellume is recalling some at-home tests after learning that they were reporting a higher-than-expected rate of false positive results indicating someone has the virus when they do not.

The Australian company has said the tests were shipped to U.S. retailers and other distributors from April through August. It published a list on its website of the lot numbers on test packages affected by the recall.

The company said about 427,000 tests are in the lots identified in the recall, and nearly 200,000 are unused. Ellume said tests from those lots may provide false positive results at a rate higher than researchers saw during clinical testing.

Ellume said it will email customers who used one of those test kits and received a positive result in the last two weeks. It recommended that people who have not scheduled another test to confirm the result should immediately do so.

The U.S. Food and Drug Administration said Tuesday in a separate statement that people who got a positive result from one of the tests should contact a care provider or urgent care location and ask for a molecular diagnostic test.

The problem was tied to a manufacturing issue, and it does not appear to affect negative results from the tests.

Ellume said about 42,000 affected tests have been used and produced positive results, both accurate and false. That represents about 1% of the 3.5 million tests the company has shipped to the U.S.