diff -r d20770229f99 -r c29fc61fb1b1 src/Pure/Tools/build.scala
--- a/src/Pure/Tools/build.scala	Sat May 26 13:36:28 2018 +0200
+++ b/src/Pure/Tools/build.scala	Sat May 26 16:52:03 2018 +0200
@@ -189,7 +189,8 @@
     isabelle.graphview.Graph_File.write(options, graph_file, deps(name).session_graph_display)
 
     private val export_tmp_dir = Isabelle_System.tmp_dir("export")
-    private val export_consumer = Export.consumer(store.open_database(name, output = true))
+    private val export_consumer =
+      Export.consumer(store.open_database(name, output = true), cache = store.xz_cache)
 
     private val future_result: Future[Process_Result] =
       Future.thread("build") {