Businessman Yim Ah Chai, 47, found it the painful way when he grappled with a pig-tailed macaque (or berok) here on Thursday evening.
Yim was checking his mailbox when the waist-high monkey jumped over the gate into his house in Taman Lake View.
“It bit my left hand and I started punching but it became more aggressive.
“I threw another punch and then I felt its teeth on my thigh,” he said.
He shouted for help but no one heard him. Yim's wife and children thought he was playing with their dog.
When he got hold of a stick, the monkey let go but was about to attack his wife who was coming out of the door.
“Luckily, it just walked away and jumped over to my neighbour’s compound before disappearing,'' he said.
Doctors told Yim that he was lucky to be wearing trousers.
“Had I been wearing shorts, the monkey's fangs could have severed the main artery and I could have succumbed to excessive bleeding,” said Yim.
He has since warned his three children, aged six to 17, not to go out of the house.