Sex with a minor amounts to rape even if the couple are married, India's top court ruled on Wednesday, closing a legal loophole that had allowed some perpetrators to escape punishment.
The age of consent and thus the legal age for girls to marry in India is 18, but millions of children are made to do so when they are much younger, particularly in poor rural areas.
India's rape laws specifically exclude married couples, which historically meant that even non-consensual sex with a minor could not be classed as rape if it took place within marriage.
But the Supreme Court said that contradicted India's strict laws on the age of consent.
It ruled that police should in future prosecute cases of marital rape if the victim was under 18 and registered a complaint within a year of the incident.
Vikram Srivastava, a lawyer who petitioned the court on the issue, welcomed the ruling which he said would give child victims some protection.
"The judgement today in two lines says that if anyone now marries a girl child below the age of 18 years and if the girl complains within a year of sexual intercourse, then that person can be prosecuted for rape," he said in comments broadcast on the NDTV news network.
"(Child marriage) is prohibited, but we all know the number of children who are married below the age of 18 years."
Many parents in India marry off their children in the hope of improving their financial security and to avoid the shame associated with pre-marital sex.
The results can be devastating, with girls dropping out of school to cook and clean for their husbands and suffering health problems from giving birth at a young age.
A separate challenge to the laws on marital rape is currently going through the Indian courts.
The government has said it opposes criminalising marital rape as this would damage the institution of marriage.