diff -r c6e9c7d140ff -r c88d1c36c9c3 src/Pure/PIDE/active.ML
--- a/src/Pure/PIDE/active.ML	Wed Jun 21 22:57:40 2017 +0200
+++ b/src/Pure/PIDE/active.ML	Thu Jun 22 14:27:13 2017 +0200
@@ -49,7 +49,7 @@
   let
     val i = serial ();
     fun abort () = Synchronized.change dialogs (Inttab.delete_safe i);
-    val promise = Future.promise abort : string future;
+    val promise = Future.promise_name "dialog" abort : string future;
     val _ = Synchronized.change dialogs (Inttab.update_new (i, promise));
     fun result_markup result = Markup.properties (explicit_id ()) (Markup.dialog i result);
   in (result_markup, promise) end;