diff -r a471730347e0 -r 460d743010bc src/Tools/Code/code_scala.ML
--- a/src/Tools/Code/code_scala.ML	Mon Oct 26 21:35:39 2020 +0100
+++ b/src/Tools/Code/code_scala.ML	Tue Oct 27 22:34:37 2020 +0100
@@ -465,7 +465,7 @@
   (Code_Target.add_language
     (target, { serializer = serializer, literals = literals,
       check = { env_var = "SCALA_HOME",
-        make_destination = fn p => Path.append p (Path.explode "ROOT.scala"),
+        make_destination = fn p => p + Path.explode "ROOT.scala",
         make_command = fn _ =>
           "isabelle_scala scalac $ISABELLE_SCALAC_OPTIONS ROOT.scala"},
       evaluation_args = Token.explode0 Keyword.empty_keywords "case_insensitive"})