Rwanda's government should review two laws banning the promotion of genocide ideology and sectarianism, Amnesty International says.
The campaign groups says the vague wording has enabled their misuse to criminalise dissent.
The government was widely criticised for using them to smother opposition in the run-up the elections won by President Paul Kagame this month.
Rwanda's justice minister told the BBC the Amnesty allegations were baseless.
The laws were introduced in the aftermath of the 1994 genocide in which an estimated 800,000 Tutsi and moderate Hutus were killed in 100 days.
In its report, Safer to Stay Silent, Amnesty said that the legislation is so ambiguous that even legal professionals struggle to define what "genocide ideology" really means.
"The results is that many chose not to speak out, not to criticise the authorities," Erwin van der Borght, head of Amnesty's Africa programme, told the BBC's Network Africa programme.
In the lead-up to the presidential elections two opposition candidates were arrested and charged with "genocide ideology" and a newspaper editor was also arrested on the same charge.
The government argues that the two laws are necessary to prevent the kind of hate-speech that helped fuel the genocide, and that could destabilise it once more.
"It's not true that the genocide ideology law was crafted with a view to being used to suppress political debate," Justice Minister Tharcisse Karugarama said.
In April, the government did say it would clarify the genocide law admitting it had some weaknesses.
Amnesty says this is a start, but argues both laws need urgent overhaul.
"Every time a country has made legislation, it does not close it to review," Mr Karugarama told the BBC.
"We review our laws on the basis of what people have said, on the basis of what people have expressed as a need; on the basis of what we see… We don't make it to satisfy Amnesty International," he said.