src/Pure/System/isabelle_system.scala

     for (name <- space_explode(':', Isabelle_System.getenv_strict(variable)))
     yield {
       def err(msg: String): Nothing =
         error("Bad entry " + quote(name) + " in " + variable + "\n" + msg)
 
-      try { Class.forName(name).asInstanceOf[Class[A]].newInstance() }
+      try {
+        Class.forName(name).asInstanceOf[Class[A]].getDeclaredConstructor().newInstance()
+      }
       catch {
         case _: ClassNotFoundException => err("Class not found")
         case exn: Throwable => err(Exn.message(exn))
       }
     }