encountered a malformed backend state file with a…

Error message

encountered a malformed backend state file with a 'state_store' block that is missing the required 'provider_supply_mode' property

What it means

ParseBackendStateFile decoded a state_store block but its required `provider_supply_mode` property is empty/missing. ProviderSupplyMode drives how Terraform sources the state-store's nested provider (built-in, managed-by-terraform, reattached, dev-override); without it later code would crash on an empty version, so parsing fails fast with a clear message instead.

Solutions

Re-run `terraform init` so the state_store block is rewritten with all required fields.
Verify you are on a Terraform/OpenTofu version that actually supports state_store — older versions never wrote this field.
Delete the corrupt file and re-init from your state_store configuration block.

Example fix

rm .terraform/terraform.tfstate
terraform init

Defensive patterns

Strategy: validation

Validate before calling

// pre-flight: require provider_supply_mode on state_store
var probe struct {
    StateStore *struct {
        Mode string `json:"provider_supply_mode"`
    } `json:"state_store"`
}
_ = json.Unmarshal(src, &probe)
if probe.StateStore != nil && probe.StateStore.Mode == "" {
    return nil, errors.New("state_store block missing provider_supply_mode; re-run `terraform init`")
}

Prevention

Stay on a Terraform/OpenTofu version that supports state_store end-to-end.
Don't hand-edit the state_store section.

When it happens

Trigger: A .terraform/terraform.tfstate with a `state_store` object that omits `provider_supply_mode`. Possible causes: hand-editing, a buggy/old fork that didn't write the field, or a file truncated mid-write.

Common situations: Pre-release or experimental state_store support that predates the field, third-party tooling that wrote an incomplete state_store block, or filesystem-level tampering.

Understand the failure class

Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

AI-assisted analysis of hashicorp/terraform@d32a084675 (2026-08-11). Data as JSON: /api/errors/441bf995c0a5f7cd. Report an issue: GitHub.

Appendix: source

Thrown at internal/command/workdir/backend_state.go:116

	var stateFile BackendStateFile
	err = json.Unmarshal(src, &stateFile)
	if err != nil {
		return nil, fmt.Errorf("invalid syntax: %w", err)
	}
	if stateFile.Backend == nil && stateFile.Remote != nil {
		// It's very unlikely to get here, but one way it could happen is
		// if this working directory was most recently used with Terraform v0.8
		// or earlier, which didn't yet include the concept of backends.
		// This error message assumes that's the case.
		return nil, fmt.Errorf("this working directory uses legacy remote state and so must first be upgraded using Terraform v0.9")
	}
	if stateFile.Backend != nil && stateFile.StateStore != nil {
		return nil, fmt.Errorf("encountered a malformed backend state file that contains state for both a 'backend' and a 'state_store' block")
	}
	if stateFile.StateStore != nil && stateFile.StateStore.ProviderSupplyMode == "" {
		// Check for this, as lacking this data can cause problems later when an empty provider version
		// is encountered. This error will make debugging much easier.
		return nil, fmt.Errorf("encountered a malformed backend state file with a 'state_store' block that is missing the required 'provider_supply_mode' property")
	}

	return &stateFile, nil
}

func EncodeBackendStateFile(f *BackendStateFile) ([]byte, error) {
	f.Version = 3 // we only support version 3
	f.TFVersion = version.SemVer.String()

	switch {
	case f.Backend != nil && f.StateStore != nil:
		return nil, fmt.Errorf("attempted to encode a malformed backend state file; it contains state for both a 'backend' and a 'state_store' block. This is a bug in Terraform and should be reported.")
	case f.Backend == nil && f.StateStore == nil:
		// This is valid - if the user has a backend state file and an implied local backend in use
		// the backend state file exists but has no Backend data.
	case f.Backend != nil:
		// Not implementing anything here - risk of breaking changes
	case f.StateStore != nil:

View on GitHub (pinned to d32a084675)