diff --git a/internal/stacks/stackruntime/internal/stackeval/planning_test.go b/internal/stacks/stackruntime/internal/stackeval/planning_test.go
index 7325b6a808..8fe80f948b 100644
--- a/internal/stacks/stackruntime/internal/stackeval/planning_test.go
+++ b/internal/stacks/stackruntime/internal/stackeval/planning_test.go
@@ -6,8 +6,10 @@ package stackeval
 import (
 	"context"
 	"fmt"
+	"strings"
 	"testing"
 
+	"github.com/davecgh/go-spew/spew"
 	"github.com/google/go-cmp/cmp"
 	"github.com/zclconf/go-cty/cty"
 	"google.golang.org/protobuf/reflect/protoreflect"
@@ -23,6 +25,7 @@ import (
 	"github.com/hashicorp/terraform/internal/stacks/stackstate/statekeys"
 	"github.com/hashicorp/terraform/internal/stacks/tfstackdata1"
 	"github.com/hashicorp/terraform/internal/terraform"
+	"github.com/hashicorp/terraform/internal/tfdiags"
 )
 
 func TestPlanning_DestroyMode(t *testing.T) {
@@ -577,3 +580,44 @@ func TestPlanning_RequiredComponents(t *testing.T) {
 		}
 	})
 }
+
+func TestPlanning_NoWorkspaceNameRef(t *testing.T) {
+	// This test verifies that a reference to terraform.workspace is treated
+	// as invalid for modules used in a stacks context, because there's
+	// no comparable single string to use in stacks context and we expect
+	// modules used in stack components to vary declarations based only
+	// on their input variables.
+	//
+	// (If something needs to vary between stack deployments then that's
+	// a good candidate for an input variable on the root stack configuration,
+	// set differently for each deployment, and then passed in to the
+	// components that need it.)
+
+	cfg := testStackConfig(t, "planning", "no_workspace_name_ref")
+	main := NewForPlanning(cfg, stackstate.NewState(), PlanOpts{
+		PlanningMode: plans.NormalMode,
+	})
+
+	inPromisingTask(t, func(ctx context.Context, t *testing.T) {
+		_, diags := testPlan(t, main)
+		if !diags.HasErrors() {
+			t.Fatal("success; want error about invalid terraform.workspace reference")
+		}
+
+		// At least one of the diagnostics must mention the terraform.workspace
+		// attribute in its detail.
+		seenRelevantDiag := false
+		for _, diag := range diags {
+			if diag.Severity() != tfdiags.Error {
+				continue
+			}
+			if strings.Contains(diag.Description().Detail, "terraform.workspace") {
+				seenRelevantDiag = true
+				break
+			}
+		}
+		if !seenRelevantDiag {
+			t.Fatalf("none of the error diagnostics mentions terraform.workspace\n%s", spew.Sdump(diags.ForRPC()))
+		}
+	})
+}
diff --git a/internal/stacks/stackruntime/internal/stackeval/testdata/sourcebundle/planning/no_workspace_name_ref/no-workspace-name-ref.tf b/internal/stacks/stackruntime/internal/stackeval/testdata/sourcebundle/planning/no_workspace_name_ref/no-workspace-name-ref.tf
new file mode 100644
index 0000000000..e911ee4453
--- /dev/null
+++ b/internal/stacks/stackruntime/internal/stackeval/testdata/sourcebundle/planning/no_workspace_name_ref/no-workspace-name-ref.tf
@@ -0,0 +1,6 @@
+output "invalid" {
+  # terraform.workspace is not available when this module is used as part
+  # of a stack component, so this should produce an error during
+  # planning.
+  value = terraform.workspace
+}
diff --git a/internal/stacks/stackruntime/internal/stackeval/testdata/sourcebundle/planning/no_workspace_name_ref/no-workspace-name-ref.tfstack.hcl b/internal/stacks/stackruntime/internal/stackeval/testdata/sourcebundle/planning/no_workspace_name_ref/no-workspace-name-ref.tfstack.hcl
new file mode 100644
index 0000000000..ac4b9e559f
--- /dev/null
+++ b/internal/stacks/stackruntime/internal/stackeval/testdata/sourcebundle/planning/no_workspace_name_ref/no-workspace-name-ref.tfstack.hcl
@@ -0,0 +1,3 @@
+component "mod" {
+  source = "./"
+}
diff --git a/internal/terraform/evaluate.go b/internal/terraform/evaluate.go
index 5a10dc7ee9..45f75dd4c6 100644
--- a/internal/terraform/evaluate.go
+++ b/internal/terraform/evaluate.go
@@ -811,6 +811,37 @@ func (d *evaluationStateData) getResourceSchema(addr addrs.Resource, providerAdd
 
 func (d *evaluationStateData) GetTerraformAttr(addr addrs.TerraformAttr, rng tfdiags.SourceRange) (cty.Value, tfdiags.Diagnostics) {
 	var diags tfdiags.Diagnostics
+
+	if d.Evaluator.Meta == nil || d.Evaluator.Meta.Env == "" {
+		// The absense of an "env" (really: workspace) name suggests that
+		// we're running in a non-workspace context, such as in a component
+		// of a stack. terraform.workspace -- and the terraform symbol in
+		// general -- is a legacy thing from workspaces mode that isn't
+		// carried forward to stacks, because stack configurations can instead
+		// vary their behavior based on input variables provided in the
+		// deployment configuration.
+		switch addr.Name {
+		case "workspace":
+			diags = diags.Append(&hcl.Diagnostic{
+				Severity: hcl.DiagError,
+				Summary:  `Invalid reference`,
+				Detail:   `The terraform.workspace attribute is only available for modules used in Terraform workspaces. Use input variables instead to create variations between different instances of this module.`,
+				Subject:  rng.ToHCL().Ptr(),
+			})
+		default:
+			// A more generic error for any other attribute name, since no
+			// others are valid anyway but it would be confusing to mention
+			// terraform.workspace here.
+			diags = diags.Append(&hcl.Diagnostic{
+				Severity: hcl.DiagError,
+				Summary:  `Invalid reference`,
+				Detail:   `The "terraform" object is only available for modules used in Terraform workspaces.`,
+				Subject:  rng.ToHCL().Ptr(),
+			})
+		}
+		return cty.DynamicVal, diags
+	}
+
 	switch addr.Name {
 
 	case "workspace":