diff -r 4c8295f2f849 -r e48d93811ed7 src/Pure/Tools/build.scala
--- a/src/Pure/Tools/build.scala	Sat Oct 03 23:01:40 2020 +0100
+++ b/src/Pure/Tools/build.scala	Mon Oct 05 21:15:58 2020 +0200
@@ -414,7 +414,7 @@
       if (result1.ok) {
         for (document_output <- proper_string(options.string("document_output"))) {
           val document_output_dir = info.dir + Path.explode(document_output)
-          Isabelle_System.mkdirs(document_output_dir)
+          Isabelle_System.make_directory(document_output_dir)
 
           val base = deps(session_name)
           File.write(document_output_dir + Path.explode("session.tex"),