A retired NYPD officer shot an innocent bystander as he fought with another man at a Queens restaurant Tuesday night, law enforcement sources said.

It’s unclear how the fracas at Frenasia — an Asian bistro in Howard Beach — began, but it escalated at about 7:15 p.m. when a 61-year-old man swung his chair at the ex-cop, 52, sources said.

The former officer then took out his gun, which sources said is legally registered to him, and fired one round — missing his intended target and striking a 31-year-old man at the eatery.

The gunshot victim was struck in the lower back. He was taken to Jamaica Hospital and is in stable condition, sources said.

Both the retired officer and the man he was fighting with were taken into custody for questioning, according to sources.