Ladies, you're going to want to pay attention to this one.

Pfizer is recalling one million packets of Lo/Ovral-28 birth control pills and its generic equivalent Norgestrel and Ethinyl Estradiol due to a manufacturing error that may have put some of the pills out of order, increasing the risk of unintended pregnancy in users, the AP reports.

The packets have expiration dates that range between July 31, 2013 and March 31, 2014 and were marketed in the U.S. by Akirmax Rx Products. Another AP piece says that company thinks that only about 30 packets were defective.

Birth control pills work by using hormones to prevent pregnancy, with 21 “active” pills and 7 inactive sugar pills. Typically, if a woman misses a single active pill she can take it the next day but missing more than one pill consecutively, Griffin says, increase the risk of contraceptive failure. But in the case of this batch, it seems, none of the pills prevented conception.

Amanda L. Chan of the Huffington Post reports that women who think they’ve gotten the defective pill packets should call their doctor right away, according to Dr. Adam Griffin of the University of Rochester Medical Center and the FDA, which also said women should “return the birth control to the pharmacy.”

She might also want to take “a pregnancy test or serum pregnancy test,” Chan writes, and notes that though taking active birth control pills after becoming pregnant “should not effect the health of her baby,” the Mayo Clinic suggests women stop taking the pill after pregnancy.