diff -r 4c8295f2f849 -r e48d93811ed7 src/Pure/Admin/build_cygwin.scala
--- a/src/Pure/Admin/build_cygwin.scala	Sat Oct 03 23:01:40 2020 +0100
+++ b/src/Pure/Admin/build_cygwin.scala	Mon Oct 05 21:15:58 2020 +0200
@@ -25,7 +25,7 @@
         val cygwin = tmp_dir + Path.explode("cygwin")
         val cygwin_etc = cygwin + Path.explode("etc")
         val cygwin_isabelle = cygwin + Path.explode("isabelle")
-        Isabelle_System.mkdirs(cygwin_isabelle)
+        Isabelle_System.make_directory(cygwin_isabelle)
 
         val cygwin_exe_name = mirror + "/setup-x86_64.exe"
         val cygwin_exe = cygwin_isabelle + Path.explode("cygwin.exe")