diff -r 84ca5e036897 -r 44fe9fe96130 src/Pure/Tools/build.scala
--- a/src/Pure/Tools/build.scala	Sat Feb 25 17:45:10 2023 +0100
+++ b/src/Pure/Tools/build.scala	Sun Feb 26 11:55:24 2023 +0100
@@ -171,9 +171,10 @@
     val results =
       Isabelle_Thread.uninterruptible {
         val engine = get_engine(build_options.string("build_engine"))
-        val build_process = engine.init(build_context)
-        val res = build_process.run()
-        Results(build_context, res)
+        using(engine.init(build_context)) { build_process =>
+          val res = build_process.run()
+          Results(build_context, res)
+        }
       }
 
     if (export_files) {