src/Tools/adhoc_overloading.ML

       "Unresolved overloading of constant" ::
       quote c ^ " :: " ^ quote (Syntax.string_of_typ ctxt' T) ::
       "in term " ::
       quote (Syntax.string_of_term ctxt' t) ::
       (if null instances then "no instances" else "multiple instances:") ::
-    map (Syntax.string_of_term ctxt') instances)
+    map (Markup.markup Markup.item o Syntax.string_of_term ctxt') instances)
     |> error
   end;
 
 (* generic data *)