src/HOL/Codatatype/Tools/bnf_gfp.ML

     val live = live_of_bnf (hd bnfs);
     val n = length bnfs; (*active*)
     val ks = 1 upto n;
     val m = live - n (*passive, if 0 don't generate a new BNF*);
     val ls = 1 upto m;
-    val b = Binding.name (mk_common_name bs);
+    val b = Binding.name (mk_common_name (map Binding.name_of bs));
 
     (* TODO: check if m, n, etc., are sane *)
 
     val deads = fold (union (op =)) Dss resDs;
     val names_lthy = fold Variable.declare_typ deads lthy;