diff --git a/common/grammar-parser.cpp b/common/grammar-parser.cpp
index e8722b52b..74152b54c 100644
--- a/common/grammar-parser.cpp
+++ b/common/grammar-parser.cpp
@@ -163,6 +163,7 @@ namespace grammar_parser {
             // the following rewrite rules:
             // S{m,n} --> S S S (m times) S'(n-m)
             //            S'(x)   ::= S S'(x-1) |
+            //            (... x definitions of these S' rules ...)
             //            S'(1)   ::= S |
             // S{m,} -->  S S S (m times) S'
             //            S'     ::= S S' |