diff --git a/src/Pure/System/setup_tool.scala b/src/Pure/System/setup_tool.scala
--- a/src/Pure/System/setup_tool.scala
+++ b/src/Pure/System/setup_tool.scala
@@ -1,37 +1,36 @@
 /*  Title:      Pure/System/setup_tool.scala
     Author:     Makarius
 
 Additional setup tools for other Isabelle distribution.
 */
 
 package isabelle
 
 
 object Setup_Tool {
   lazy val services: List[Setup_Tool] =
     Isabelle_System.make_services(classOf[Setup_Tool])
 
   def init(other_isabelle: Other_Isabelle, verbose: Boolean = false): Unit =
     services.foreach(_.init(other_isabelle, verbose = verbose))
 }
 
-abstract class Setup_Tool(tool: String)
+abstract class Setup_Tool(tool: String, val variable: String)
 extends Isabelle_System.Service {
   override def toString: String = tool
 
-  val variable: String = "ISABELLE_" + Word.uppercase(tool)
   val files: List[Path] = List(Path.explode("lib/Tools") + Path.basic(tool))
 
   def test(other_isabelle: Other_Isabelle): Boolean =
     other_isabelle.getenv(variable) == "true" &&
     files.exists(p => (other_isabelle.isabelle_home + p).is_file)
 
   def run(other_isabelle: Other_Isabelle, verbose: Boolean = false): Unit =
     other_isabelle.bash("bin/isabelle " + Bash.string(tool), echo = verbose)
 
   def init(other_isabelle: Other_Isabelle, verbose: Boolean = false): Unit =
     if (test(other_isabelle)) run(other_isabelle, verbose = verbose)
 }
 
-class GHC_Setup extends Setup_Tool("ghc_setup")
-class OCaml_Setup extends Setup_Tool("ocaml_setup")
+class GHC_Setup extends Setup_Tool("ghc_setup", "ISABELLE_GHC_SETUP")
+class OCaml_Setup extends Setup_Tool("ocaml_setup", "ISABELLE_OCAML_SETUP")