diff -r cb643a1a5313 -r def3ec9cdb7e src/Pure/Tools/rail.ML
--- a/src/Pure/Tools/rail.ML	Sun Mar 10 15:31:24 2019 +0100
+++ b/src/Pure/Tools/rail.ML	Sun Mar 10 21:12:29 2019 +0100
@@ -118,7 +118,7 @@
 
 val scan_token =
   scan_space >> token Space ||
-  Comment.scan >> (fn (kind, ss) => token (Comment kind) ss)||
+  Comment.scan_inner >> (fn (kind, ss) => token (Comment kind) ss) ||
   Antiquote.scan_antiq >> antiq_token ||
   scan_keyword >> (token Keyword o single) ||
   Lexicon.scan_id >> token Ident ||