The Supreme Court on Thursday extended a measure of fairness and clarity to a sentencing law that has been markedly unfair since its enactment. The ruling defining who is covered by less stringent penalties for crack-cocaine convictions goes some distance to correct a blatant injustice in criminal sentencing that has fallen far too heavily on poor and minority offenders.

In 1986, Congress created an unjustifiable distinction when it set federal mandatory minimum sentences that applied to people convicted of crimes involving cocaine. The Anti-Drug Abuse Act set the threshold for imposing a five-year prison sentence for possession of powder cocaine with intent to distribute at 500 grams. For the same offense involving crack cocaine, the same drug cooked into solid form, the legislation lowered the threshold for the five-year sentence to a mere 5 grams, a 100-to-1 disparity in penalties.

It quickly became apparent the law had a disproportionate racial impact. African-Americans tended to favor crack cocaine, which is cheaper. As a result, minority offenders received longer sentences for smaller amounts of crack than white offenders convicted of powder cocaine offenses.

The Fair Sentencing Act, enacted in 2010, addressed the clear injustice in sentencing, nearly a quarter-century later. The legislation retained the threshold for powder cocaine at 500 grams for a five-year term in federal prison (5,000 grams for a 10-year sentence), but raised the amount of crack necessary to trigger the five- and 10-year minimums from 5 grams to 28 grams and from 50 grams to 280 grams.

It was not clear from the law or from the subsequent sentencing guidelines issued by the U.S. Sentencing Commission whether the more lenient penalties apply to offenders other than those who committed crack offenses after the law took effect on Aug. 3, 2010. The high court ruling last week provided essential clarification. A 5-4 majority concluded the 2010 law applies to offenders who were arrested or convicted but had not been sentenced on Aug. 3, 2010. Also covered are offenders sentenced between Aug. 3 and Nov. 1, 2010, when new sentencing guidelines went into effect.

The 2010 legislation reduced an egregious disparity. It did not eliminate the basic unfairness. The ruling has broadened the law’s application, making a bad situation a little less unjust.