src/Pure/Thy/thy_resources.scala

         val import_names =
           theories.map(thy =>
             resources.import_name(qualifier, master_directory(master_dir), thy) -> Position.none)
         resources.dependencies(import_names, progress = progress).check_errors.theories
       }
-      val dep_theories_set = dep_theories.toSet
 
       val use_theories_state = Synchronized(Use_Theories_State())
 
       def check_result(beyond_limit: Boolean = false)
       {

         val delay_commit_clean =
           Standard_Thread.delay_first(commit_clean_delay max Time.zero) {
             val clean = use_theories_state.value.already_committed.keySet
             resources.clean_theories(session, id, clean)
           }
+
+        val dep_theories_set = dep_theories.toSet
 
         Session.Consumer[Session.Commands_Changed](getClass.getName) {
           case changed =>
             if (changed.nodes.exists(dep_theories_set)) {
               val snapshot = session.snapshot()