diff -r f249b5c0fea2 -r 16aa085f9353 src/Pure/Tools/debugger.ML
--- a/src/Pure/Tools/debugger.ML	Sun Apr 05 13:19:29 2020 +0200
+++ b/src/Pure/Tools/debugger.ML	Sun Apr 05 13:24:12 2020 +0200
@@ -22,7 +22,7 @@
   if msg = "" then ()
   else
     Output.protocol_message
-      (Markup.debugger_output (Isabelle_Thread.the_name ()))
+      (Markup.debugger_output (Isabelle_Thread.get_name ()))
       [XML.Text (Markup.markup (kind, Markup.serial_properties (serial ())) msg)];
 
 val writeln_message = output_message Markup.writelnN;
@@ -250,7 +250,7 @@
         (SOME (fn (_, break) =>
           if not (is_debugging ()) andalso (! break orelse is_break () orelse is_stepping ())
           then
-            (case Isabelle_Thread.get_name () of
+            (case try Isabelle_Thread.get_name () of
               SOME thread_name => debugger_loop thread_name
             | NONE => ())
           else ()))));