diff -r fc363a3b690a -r 678e1c9eb009 src/Pure/System/scala.scala
--- a/src/Pure/System/scala.scala	Thu Jul 15 16:35:45 2021 +0200
+++ b/src/Pure/System/scala.scala	Thu Jul 15 17:33:06 2021 +0200
@@ -80,12 +80,11 @@
   /** compiler **/
 
   def class_path(): List[String] =
-    Library.distinct(
-      for {
-        prop <- List("isabelle.scala.classpath", "java.class.path")
-        elems = System.getProperty(prop, "") if elems.nonEmpty
-        elem <- space_explode(JFile.pathSeparatorChar, elems) if elem.nonEmpty
-      } yield elem)
+    for {
+      prop <- List("isabelle.scala.classpath", "java.class.path")
+      elems = System.getProperty(prop, "") if elems.nonEmpty
+      elem <- space_explode(JFile.pathSeparatorChar, elems) if elem.nonEmpty
+    } yield elem
 
   object Compiler
   {