diff --git a/dagflow/dagflow.py b/dagflow/dagflow.py
index 2c06260..24b26aa 100644
--- a/dagflow/dagflow.py
+++ b/dagflow/dagflow.py
@@ -358,7 +358,7 @@ where backid=${backid}$
 				for e in on_array:
 					nnodes.append((edge['to'], str(e)))
 			else:
-				nnodes.append(edge['to'], None)
+				nnodes.append((edge['to'], None))
 
 		for node_id, ctx_ext in nnodes:
 			node = dsl['nodes'][node_id]