diff -r 9a3b4cca6d0b -r 8d548b8f63ca src/Pure/Admin/build_jdk.scala
--- a/src/Pure/Admin/build_jdk.scala	Tue Jan 29 21:56:40 2019 +0100
+++ b/src/Pure/Admin/build_jdk.scala	Tue Jan 29 22:47:45 2019 +0100
@@ -20,7 +20,7 @@
 
   def detect_version(s: String): String =
   {
-    val Version_Dir_Entry = """^jdk-(\d+\+\d+)$""".r
+    val Version_Dir_Entry = """^jdk-([0-9.]+\+\d+)$""".r
     s match {
       case Version_Dir_Entry(version) => version
       case _ => error("Cannot detect JDK version from " + quote(s))