diff --git a/dynet/lstm.cc b/dynet/lstm.cc
index 13e93a62a..ba7fd8272 100644
--- a/dynet/lstm.cc
+++ b/dynet/lstm.cc
@@ -441,6 +441,7 @@ void VanillaLSTMBuilder::serialize(Archive& ar, const unsigned int) {
   ar & params;
   ar & layers;
   ar & dropout_rate;
+  ar & hid;
 }
 DYNET_SERIALIZE_IMPL(VanillaLSTMBuilder);