diff --git a/terraform/transform_expand.go b/terraform/transform_expand.go
index 85d6602063..440c522f39 100644
--- a/terraform/transform_expand.go
+++ b/terraform/transform_expand.go
@@ -1,6 +1,7 @@
 package terraform
 
 import (
+	"fmt"
 	"log"
 
 	"github.com/hashicorp/terraform/dag"
@@ -59,3 +60,26 @@ func (n *GraphNodeBasicSubgraph) Name() string {
 func (n *GraphNodeBasicSubgraph) Subgraph() *Graph {
 	return n.Graph
 }
+
+func (n *GraphNodeBasicSubgraph) Flatten(p []string) (dag.Vertex, error) {
+	return &graphNodeBasicSubgraphFlat{
+		GraphNodeBasicSubgraph: n,
+		PathValue:              p,
+	}, nil
+}
+
+// Same as GraphNodeBasicSubgraph, but for flattening
+type graphNodeBasicSubgraphFlat struct {
+	*GraphNodeBasicSubgraph
+
+	PathValue []string
+}
+
+func (n *graphNodeBasicSubgraphFlat) Name() string {
+	return fmt.Sprintf(
+		"%s.%s", modulePrefixStr(n.PathValue), n.GraphNodeBasicSubgraph.Name())
+}
+
+func (n *graphNodeBasicSubgraphFlat) Path() []string {
+	return n.PathValue
+}