An op shop in Melbourne mistakenly sold a bloke’s expensive road bike while he was browsing in the store.

The bloke, 18-year-old Joel Larter, told the Herald Sun that he left his Fuji brand bike — worth around $1000 — just inside the Keysborough store's entrance with the permission of a staff member.

However while he was looking for clothes in the back, another worker sold the bike for just $20, thinking it was a donation.

“Apparently a passer-by saw the bike inside the store and asked if they could purchase it,” Larter told the Herald Sun.

“I spoke to the manager and all she could tell me was that a man had paid cash.”

The management of the Salvation Army store organised a payout of $170 after assessing prices of other Fuji bikes on Gumtree.