question with aws ec2 exact_count

Thought the task below would create 1 instance with the count_tag “demo”, only if there wasn’t one running, but it’s creating a new instance every time.
Am I using exact_count incorrectly?

  • name: spin up ec2 instance
    ec2:
    count_tag: demo
    exact_count: 1
    image: ami-60b6c60a
    region: us-east-1
    type: t2.nano
    wait: yes

Using ansible 2.0.0.2 and boto 2.39.0