diff --git a/frame_serialize/CBORStream2Serializer.cpp b/frame_serialize/CBORStream2Serializer.cpp
index 571180ea..25a53729 100644
--- a/frame_serialize/CBORStream2Serializer.cpp
+++ b/frame_serialize/CBORStream2Serializer.cpp
@@ -417,7 +417,7 @@ inline void CBOR_ENC(CborEncoder &encoder, const char* key, const UnitCell &val)
 inline void CBOR_ENC(CborEncoder &encoder, const char* key, const LatticeMessage &val) {
     CborEncoder mapEncoder;
     cborErr(cbor_encode_text_stringz(&encoder, key));
-    cborErr(cbor_encoder_create_map(&encoder, &mapEncoder, 4));
+    cborErr(cbor_encoder_create_map(&encoder, &mapEncoder, 3));
     CBOR_ENC(mapEncoder, "centering", std::string(1, val.centering));
     CBOR_ENC(mapEncoder, "niggli_class", val.niggli_class);
     const char* cs_name = "triclinic";