A 58-year-old man was arrested on Monday afternoon, for allegedly raping his two-year-old stepchild in KwaMbonambi, outside Mtubatuba, in northern Zululand.
Police spokesman Captain Jabulani Mdletshe said the child's mother had asked a friend to look after her children while she was away.
"The friend found the suspect, the child's stepfather, at home but thought nothing of it and went to bed," he said.
Mdletshe said the friend was awakened later in the night by the child's screams.
When she went to investigate she saw the suspect crouching behind the baby's back, wiping himself off.
"Because she was afraid she pretended not to have noticed him," Mdletshe said. "In the morning she told her friend what had happened.
"The child's mother asked a neighbour to inspect the child since she was not convinced her boyfriend could do such a thing.
"The granny confirmed the child had been raped."
The man was arrested by the police and the child taken to hospital for treatment.
The man appeared in court briefly and the case was postponed to Tuesday.