diff -r 84990c95712d -r 97e8f4c938bf src/Pure/Thy/document_build.scala
--- a/src/Pure/Thy/document_build.scala	Wed Jul 27 09:03:06 2022 +0200
+++ b/src/Pure/Thy/document_build.scala	Wed Jul 27 09:27:40 2022 +0200
@@ -155,10 +155,7 @@
 
     def get_engine(): Engine = {
       val name = document_build
-      val (files, classloader) = Isabelle_System.make_classloader(classpath)
-      val more_services =
-        files.flatMap(file => Isabelle_System.init_services_jar(File.path(file), classloader))
-      Isabelle_System.make_services(classOf[Engine], more_services = more_services)
+      Classpath(jar_contents = classpath).make_services(classOf[Engine])
         .find(_.name == name).getOrElse(error("Bad document_build engine " + quote(name)))
     }