A Canberra man has been fined for possessing cannabis while serving jail time for a series of traffic offences

Marion Tom Parlov, 47, was caught with the drug in his cell at the Symonston Periodic Detention Centre in Canberra's south.

The court heard two guards smelt the odour, before finding Parlov in the cell bent over a wash basin being sick.

The drugs were burning in a drink can.

Parlov admitted he found the drugs in a clip seal bag on the ground after he returned from a work party that day.

He said he knew the guards were nearby and admitted it was a silly thing to do.

He told the court you would have to be stupid to bring the drugs into the jail.

He also told the court he had been made ill by the drugs which he believed may have been there a while.

Magistrate Peter Morrison accepted it was an opportunistic crime and fined Parlov $300.