src/Pure/PIDE/document.ML

--- a/src/Pure/PIDE/document.ML	Thu Jun 22 14:27:13 2017 +0200
+++ b/src/Pure/PIDE/document.ML	Thu Jun 22 15:20:32 2017 +0200
@@ -371,7 +371,7 @@
     let
       val id = Document_ID.print command_id;
       val span =
-        Lazy.lazy (fn () =>
+        Lazy.lazy_name "Document.define_command" (fn () =>
           Position.setmp_thread_data (Position.id_only id)
             (fn () =>
               let