Handle s3 backends whilst indexing without Terraform credentials

If a terrareg instance doesn't have access AWS credentials configured, initialising terraform results in:

Initializing the backend...
╷
│ Error: error configuring S3 Backend: no valid credential sources for S3 Backend found.
│
│ Please see https://www.terraform.io/docs/language/settings/backends/s3.html
│ for more information about providing credentials.
│
│ Error: NoCredentialProviders: no valid providers in chain. Deprecated.
│ For verbose messaging see aws.Config.CredentialsChainVerboseErrors
│
│
│
╵

Is there a way to get around this?