Diane Abbott has faced ridicule after she claimed 16-year-olds should be allowed to vote if they are able to fight for their country.
The legal age a soldier can be sent to a combat zone is 18.
The shadow home secretary made the blunder ahead of the second reading of a private members' bill seeking to reduce the voting age to 16 on Friday.
The bill was later shelved under Commons laws that rule items must reach a vote before 2.30pm on a Friday with Labour accusing the Tories of filibustering to block the party's attempt to lower the legal voting age.
Speaking in a video posted on her official social media accounts, the Labour MP for Hackney North and Stoke Newington said: "I believe in votes at 16. If you're old enough to fight for your country, you are old enough to vote.
"The Labour Party believes young people should have a say over their future."
British Army soldiers can sign up at the age of 16 but they cannot be sent to fight in a war zone or engage in a hostile situation until the age of 18.
One person criticised Ms Abbott on Facebook, writing: "You can't fight at 16. You can join the forces but definitely no fighting until you're 18. That is international law. Straight away wrong with a simple fact."
Another joked: "She was never good with numbers."
James tweeted: "Thankfully 16 year olds are not allowed to fight for their country @HackneyAbbott."
Another person said: "You have probably just upset a lot of 16 year olds that they may have to go to war."
A man wrote: "Sixteen year olds don't fight on the frontline... yet again Abbott doesn't know the facts."
It comes after Ms Abbott floundered over Labour's plans for police funding during two separate interviews during the election campaign.
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