Yadav, who was among the early voters, marked his vote in favour of Sangma instead of Mukherjee but as soon as he realised the mistake he pointed it out to the polling officers and sought a fresh ballot paper, sources said.
The SP chief marked his correct preference on the fresh ballot paper issued to him by the polling officer.
The ballot paper carrying the incorrect entry made by Yadav has been deposited with the polling officer, the sources said.
The SP had backed Mukherjee after giving the ruling UPA some anxious moments as Yadav had initially teamed up with Trinamool Congress chief Mamata Banerjee and proposed the names of Prime Minister Manmohan Singh, former Speaker Somnath Chatterjee and former President A P J Abdul Kalam as possible candidates for the 14th Presidential election.
Yadav announced his support to Mukherjee later.
