County officials say the error caused only one side of the ballot to print.
Officials say this impacts 16,000 general election mail-in ballots.
NPC, the company who prints the ballots noticed the error, CEO Chip Gallaher said:
"We sincerely regret that this happened and are working with the County and State to ensure impacted voters receive a new ballot. Once the error was recognized, we immediately stopped production and began to investigate. Our investigation determined that a programming error caused the back page of the ballot to be omitted."
Montgomery County is asking anyone who receives the faulty ballot to return the ballot and envelopes.
Officials say new mail-in ballots will be re-issued automatically and expected to be mailed by next week.