When domestic violence offenders are required to relinquish their guns, instead of simply being barred from owning firearms, the risk that those offenders may kill their partners goes down, a new study finds.

The paper, described in the Annals of Internal Medicine, highlights a simple method for lowering the risk women face of being killed by an intimate partner: Enforce the laws already in place.

Each year, the study authors point out, more than 1,800 people are killed by their intimate partners – current or former spouses or people they dated, for example. About half of those killings are carried out with a gun.

Roughly 85 percent of those victims are women. In fact, nearly half of the women killed in the U.S. each year are killed not by a stranger, but by an intimate partner.

Firearms play a significant role in these domestic violence homicides – a pattern that the law has tried to address for decades. The 1994 Violence Against Women Act banned gun ownership for people with permanent restraining orders because of intimate-partner violence, or IPV. And a 1968 law banning gun ownership for those with an IPV-related felony was extended to include misdemeanors in 1996.

In theory, these laws should be enough; in practice, they’re hard to enforce on the federal level. So state laws have sprung up to fill the gap.

The problem is, the state laws were modeled after the federal law, which has a gaping loophole: While offenders are not allowed to own a gun, they aren’t explicitly compelled by the law to give up any guns they already have.

In states that simply banned gun possession, the gun-related intimate-partner homicide rate did not drop by a statistically significant amount. But in the states that required offenders to surrender their guns – including California, Massachusetts and New York – that rate dropped by a full 14 percent.