src/Tools/jEdit/src/jedit_main.scala

     /* startup */
 
     System.setProperty("jedit.home",
       Isabelle_System.platform_path(Path.explode("$JEDIT_HOME/dist")))
 
+    System.setProperty("scala.home",
+      Isabelle_System.platform_path(Path.explode("$SCALA_HOME")))
+
     jEdit.main(jedit_options ++ jedit_settings ++ more_args)
   }
 }