diff -r 3a196e63a80d -r 276b07a1b5f5 src/HOL/Tools/typedef.ML
--- a/src/HOL/Tools/typedef.ML	Sun Aug 04 12:21:13 2024 +0200
+++ b/src/HOL/Tools/typedef.ML	Sun Aug 04 13:14:33 2024 +0200
@@ -218,7 +218,7 @@
       |> Typedecl.typedecl {final = false} (name, args, mx)
       ||> Variable.declare_term set;
 
-    val Type (full_name, _) = newT;
+    val full_name = dest_Type_name newT;
 
 
     (* axiomatization *)