diff --git a/pydot_ng/__init__.py b/pydot_ng/__init__.py
index 7f97ccd..344379d 100644
--- a/pydot_ng/__init__.py
+++ b/pydot_ng/__init__.py
@@ -1621,7 +1621,7 @@ def __init__(self, graph_name='subG', obj_dict=None,
 
         if obj_dict is None:
             self.obj_dict['type'] = 'subgraph'
-            self.obj_dict['name'] = 'cluster_' + graph_name
+            self.obj_dict['name'] = quote_if_necessary('cluster_' + graph_name)
 
         self.create_attribute_methods(CLUSTER_ATTRIBUTES)