diff -r a150dd0ebdd3 -r a5ff9cf61551 src/Pure/Tools/build_job.scala
--- a/src/Pure/Tools/build_job.scala	Fri Dec 30 16:23:32 2022 +0100
+++ b/src/Pure/Tools/build_job.scala	Fri Dec 30 20:26:28 2022 +0100
@@ -31,10 +31,8 @@
     }
     yield {
       val master_dir =
-        Thy_Header.split_file_name(thy_file) match {
-          case Some((dir, _)) => dir
-          case None => error("Cannot determine theory master directory: " + quote(thy_file))
-        }
+        Url.strip_base_name(thy_file).getOrElse(
+          error("Cannot determine theory master directory: " + quote(thy_file)))
       val node_name =
         Document.Node.Name(thy_file, master_dir = master_dir, theory = theory_context.theory)