diff --git a/doc/langref.html.in b/doc/langref.html.in
index 551f3ff76..769f6d586 100644
--- a/doc/langref.html.in
+++ b/doc/langref.html.in
@@ -5667,7 +5667,7 @@ pub const TypeInfo = union(TypeId) {
 
     pub const Union = struct {
         layout: ContainerLayout,
-        tag_type: type,
+        tag_type: ?type,
         fields: []UnionField,
         defs: []Definition,
     };