diff -r 31ee094dea3d -r 56c51f8a118b src/Pure/Admin/build_cygwin.scala
--- a/src/Pure/Admin/build_cygwin.scala	Wed Mar 20 22:01:12 2019 +0100
+++ b/src/Pure/Admin/build_cygwin.scala	Wed Mar 20 22:41:50 2019 +0100
@@ -9,7 +9,7 @@
 
 object Build_Cygwin
 {
-  val default_mirror: String = "https://isabelle.sketis.net/cygwin_2018"
+  val default_mirror: String = "https://isabelle.sketis.net/cygwin_2019"
 
   val packages: List[String] =
     List("curl", "nano", "perl", "perl-libwww-perl", "rlwrap", "unzip")