diff --git a/include/onnxruntime/core/graph/graph.h b/include/onnxruntime/core/graph/graph.h
index c4c1e71356..cafbf007d1 100644
--- a/include/onnxruntime/core/graph/graph.h
+++ b/include/onnxruntime/core/graph/graph.h
@@ -298,8 +298,12 @@ class Node {
   /** Sets the execution ProviderType that this Node will be executed by. */
   void SetExecutionProviderType(ProviderType execution_provider_type);
 
-  /** Gets the NodeProto representation of this Node. */
-  void ToProto(ONNX_NAMESPACE::NodeProto& proto) const;
+  /** Gets the NodeProto representation of this Node. 
+  @param update_subgraphs Update the GraphProto values for any subgraphs in the returned NodeProto.
+                          If graph optimization has been run this is most likely required
+                          to ensure the complete Graph is valid.
+  */
+  void ToProto(ONNX_NAMESPACE::NodeProto& proto, bool update_subgraphs = false) const;
 
   /** Call the provided function for all explicit inputs, implicit inputs, and outputs of this Node.
       If the NodeArg is an explicit or implicit input, is_input will be true when func is called.
diff --git a/onnxruntime/core/graph/graph.cc b/onnxruntime/core/graph/graph.cc
index e70faff417..d06b1eccb1 100644
--- a/onnxruntime/core/graph/graph.cc
+++ b/onnxruntime/core/graph/graph.cc
@@ -399,21 +399,25 @@ void Node::SetExecutionProviderType(ProviderType execution_provider_type) {
   execution_provider_type_ = execution_provider_type;
 }
 
-void Node::ToProto(NodeProto& proto) const {
-  // Set name.
+void Node::ToProto(NodeProto& proto, bool update_subgraphs) const {
   proto.set_name(name_);
-  // Set op type.
   proto.set_op_type(op_type_);
-  // Set op domain;
-  proto.set_domain(domain_);
-  // Set doc string.
-  proto.set_doc_string(description_);
+
+  if (!domain_.empty())
+    proto.set_domain(domain_);
+
+  if (!description_.empty())
+    proto.set_doc_string(description_);
 
   // Set attributes.
   proto.clear_attribute();
   for (const auto& attribute : attributes_) {
     const gsl::not_null<AttributeProto*> attr{proto.add_attribute()};
-    *attr = attribute.second;
+    *attr = attribute.second;  // copy
+    if (update_subgraphs && attr->has_g()) {
+      attr->clear_g();
+      *attr->mutable_g() = attr_to_subgraph_map_.find(attribute.first)->second->ToGraphProto();
+    }
   }
 
   // Set inputs' definitions.
@@ -2327,7 +2331,9 @@ void Graph::ToGraphProtoInternal(ONNX_NAMESPACE::GraphProto& graph_proto) const
   for (auto& node_idx : graph_viewer.GetNodesInTopologicalOrder()) {
     const gsl::not_null<NodeProto*> node_proto{graph_proto.add_node()};
     const gsl::not_null<const Node*> p_node{GetNode(node_idx)};
-    p_node->ToProto(*node_proto);
+    // we need to update any GraphProto attributes for subgraphs so that any changes made by things
+    // such as the optimizers are captured. otherwise we can end up saving an invalid graph.
+    p_node->ToProto(*node_proto, /* update_subgraphs */ true);
   }
 }