The two men approached the man's home on Saturday and pointed a gun at Windell Haynes, who was on the front porch.
When of the robbers tried to grab a chain from around the veteran's neck, Haynes hit him with his cane.
One of the robbers then accidentally shot his accomplice in the stomach. The wounded man was sent to the hospital with minor injuries, while the other robber ran away, El Nuevo Herald reported.
Haynes said he stopped another robbery in 2000, when he attacked a man who tried to steal his money at an ATM.
"They messed with the wrong one," Eddie Haynes, Windell's brother, said.
Police said they are investigating the incident.