Russia's Constitutional Court on Friday ordered a review of the conviction of prominent anti-Kremlin activist Ildar Dadin and said a law that criminalized protests had to be applied more proportionately.
Though the ruling did not strike down the law, which human rights activists have called draconian, it may make it harder to jail peaceful protesters as Russia gears up for a presidential election next year.
Kremlin-watchers widely expect President Vladimir Putin to run again, for what would be his fourth term, though he has not yet confirmed if he will do so.
Dadin, 34, was sentenced to three years in prison – reduced to two and a half on appeal - in December 2015 for a series of peaceful one-man protests against the Kremlin.
He was the first person to be jailed under a new law, introduced in 2014 after big anti-Kremlin protests, that made it a crime to violate protest rules more than twice in 180 days.
The court, which sits in St. Petersburg, ruled that the law should stay in place, but ordered a review of Dadin's case and added, in a legal opinion:
"If the violation of the law ... did not cause or include a genuine threat to cause harm, but was in essence illegal from a purely formal point of view, such a violation cannot be regarded as representing a criminal danger to society or attract a criminal sentence."
Dadin's wife, Anastasia Zotova, welcomed the review of his case on social media but said the court should have scrapped the protest law.
Russian rights activists regard Dadin, an outspoken critic of Putin and his policies, as a political prisoner.
Dadin said in November he was being tortured in prison and feared for his life.
Officials at the jail dismissed his allegations, but he was subsequently moved to a different prison.