diff --git a/xtask/src/codegen/rust.ungram b/xtask/src/codegen/rust.ungram
index 833ffd9e01..7f3063efb9 100644
--- a/xtask/src/codegen/rust.ungram
+++ b/xtask/src/codegen/rust.ungram
@@ -82,10 +82,6 @@ StructDef =
   | TupleFieldDefList WhereClause? ';'
   )
 
-UnionDef =
-  Attr* Visibility? 'union' Name GenericParamList? WhereClause?
-  RecordFieldDefList
-
 RecordFieldDefList =
  '{' fields:RecordFieldDef* '}'
 
@@ -102,6 +98,11 @@ FieldDefList =
   RecordFieldDefList
 | TupleFieldDefList
 
+
+UnionDef =
+  Attr* Visibility? 'union' Name GenericParamList? WhereClause?
+  RecordFieldDefList
+
 EnumDef =
   Attr* Visibility? 'enum' Name GenericParamList? WhereClause?
   variant_list:EnumVariantList