Referencing Serverless Output returns "[object Object]" instead of arn

I'm using State Machines for the first time, and I'm having trouble referencing the State Machine arn in my Lambda function. I've tried following this article and the docs, but I must be missing something, because instead of the arn, I'm getting "[object Object]".

Environment Variable:

  environment:
    EMAIL_STATE_MACHINE: ${self:resources.Outputs.EmailQueueStateMachine.Value}

Output:

  Outputs:
    EmailQueueStateMachine:
      Description: The ARN of the email delivery state machine
      Value:
        Ref: EmailQueueStateMachine

State Machine:

stepFunctions:
  stateMachines:
    ReportDeliveryEmailQueueStateMachine:
      name: emailQueueStateMachine
      id: EmailQueueStateMachine
      dependsOn:
        - EmailTemplatesDynamoDbTable
      definition:
       <definition> 

Everything I've read has this same setup, so I know I must be missing something obvious.