diff -r ddefb18b5b88 -r 8e4731a2a041 src/Pure/General/scan.scala
--- a/src/Pure/General/scan.scala	Fri Jul 05 00:21:47 2024 +0200
+++ b/src/Pure/General/scan.scala	Fri Jul 05 10:55:02 2024 +0200
@@ -436,7 +436,7 @@
     reader.isInstanceOf[Byte_Reader]
 
   def reader_decode_utf8(is_utf8: Boolean, s: String): String =
-    if (is_utf8) UTF8.decode_permissive(Bytes.raw(s)) else s
+    if (is_utf8) Bytes.raw(s).text else s
 
   def reader_decode_utf8(reader: Reader[Char], s: String): String =
     reader_decode_utf8(reader_is_utf8(reader), s)