Lawmakers on Beacon Hill have hammered out a compromise three-strikes bill that would force repeat criminals to serve more time in prison. Some new tough-on-crime law is likely to be enacted, given that both the House and Senate have passed similar bills by overwhelming margins. But lawmakers ought to make sure the final product doesn’t increase crowding at state prisons or permit unjust sentences for borderline felonies. The compromise bill doesn’t meet that standard.

A three-strikes law has the right intention: ensuring that habitual offenders stay behind bars in order to reduce crime. But the House and Senate bills both ran the risk of forcing judges to hand down harsh sentences even when undeserved. They would have made anyone convicted three times of any of 60 offenses subject to long sentences without parole. The list of crimes, which once included nonviolent offenses such as breaking and entering at night alongside the most violent ones, was too broad. The decades-long sentences that would have resulted would only exacerbate prison crowding.

To their credit, legislators have spent the past few months trying to whittle the list of 60 crimes down to the worst crimes, a step that would allay some of the unwanted consequences. One proposal that is crucial to a fair bill is for judges to be empowered to allow parole eligibility for a third-strike offender where there’s a compelling interest in justice. Governor Patrick should reject a final bill that lacks this provision.

The compromise appears to include some of Patrick’s proposal to reduce existing mandatory sentencing laws for nonviolent drug offenses, a major contributor to increased prison costs and crowding. The measure also adopts a useful Senate provision to shrink the drug-free school zones where crimes result in stiff mandatory sentences, regardless of whether a crime actually endangered children.

The horrific events that sparked the push for tougher sentences — the murder of Woburn police officer Jack Maguire by a paroled felon and the rape and murder of Melissa Gosule by a repeat offender — may have been avoided by a tougher sentencing code, so it’s easy to see why lawmakers want to act. But the fact that Texas and other Southern states have cut their own tough sentencing laws in favor of alternatives like treatment programs, and have seen less prison crowding as a result, should give local policymakers pause. Now that lawmakers here are set on passing a three-strikes law, they need to avoid the excesses that have prompted other states to change course.