The US Supreme Court ruled Monday that an international chemical weapons treaty should not have been invoked against a woman who tried to poison her rival in a love triangle.

In November, the top panel considered the case of an American microbiologist who put arsenic and potassium dichromate on the mailbox and car controls of a friend who had an adulterous fling with her husband and got pregnant.

Carol Bond was arrested in the failed attempt to kill the other woman, pleading guilty in 2007 to two counts of the federal crime of having used a chemical weapon.

She was sentenced to six years in prison and released in 2012.

Bond then appealed her conviction to the US Supreme Court, saying the law was supposed to stop terrorists from using chemical arms, not to prosecute individuals.

In its ruling Monday, the Supreme Court found that authorities had indeed gone too far.

"The global need to prevent chemical warfare does not require the federal government to reach into the kitchen cupboard or to treat a local assault with a chemical irritant as the deployment of a chemical weapon," the nine justices wrote in their unanimous decision.

If this were the case, they added, "any parent would be guilty of a serious federal offense -- possession of a chemical weapon -- when, exasperated by the children's repeated failure to clean the goldfish tank, he considers poisoning the fish with a few drops of vinegar."

At November's hearing, several justices had fretted that the list of potentially harmful chemicals would be long, with Justice Samuel Alito even jokingly asking if he would be at risk of prosecution after handing out Halloween candy bars since "chocolate is poison to dogs."

"The chemicals at issue here bear little resemblance to those whose prohibition was the object of an international convention," wrote Chief Justice John Roberts in Monday's decision.

"The government's reading ... would transform a statute concerned with acts of war, assassination, and terrorism into a massive federal anti-poisoning regime that reaches the simplest of assaults."