diff --git a/hcl2template/parser.go b/hcl2template/parser.go
index 82372bac1..a11c5dd15 100644
--- a/hcl2template/parser.go
+++ b/hcl2template/parser.go
@@ -420,6 +420,10 @@ func (cfg *PackerConfig) buildPrereqsDAG() (*dag.AcyclicGraph, error) {
 		}
 	}
 
+	if err := retGraph.Validate(); err != nil {
+		return nil, err
+	}
+
 	return &retGraph, nil
 }
 
diff --git a/internal/dag/dag.go b/internal/dag/dag.go
index 118d4bf1b..e212135a8 100644
--- a/internal/dag/dag.go
+++ b/internal/dag/dag.go
@@ -127,13 +127,8 @@ func (g *AcyclicGraph) TransitiveReduction() {
 	}
 }
 
-// Validate validates the DAG. A DAG is valid if it has a single root
-// with no cycles.
+// Validate validates the DAG. A DAG is valid if it has no cycles or self-referencing vertex.
 func (g *AcyclicGraph) Validate() error {
-	if _, err := g.Root(); err != nil {
-		return err
-	}
-
 	// Look for cycles of more than 1 component
 	var err error
 	cycles := g.Cycles()