diff --git a/lisp/simple.el b/lisp/simple.el
index 6bc3bc5304..cf537265bd 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -4102,7 +4102,8 @@ list-processes--refresh
                       (null (process-thread p))
                       (not (fboundp 'thread-name))) "--")
                     ((eq (process-thread p) main-thread) "Main")
-                    ((thread-name (process-thread p)))))
+                    ((thread-name (process-thread p)))
+                    (t "--")))
 		  (cmd
 		   (if (memq type '(network serial))
 		       (let ((contact (process-contact p t)))