diff --git a/highlighters/main/main-highlighter.zsh b/highlighters/main/main-highlighter.zsh
index 87bc229..c3cb7a9 100644
--- a/highlighters/main/main-highlighter.zsh
+++ b/highlighters/main/main-highlighter.zsh
@@ -568,7 +568,9 @@ _zsh_highlight_main_highlighter_highlight_list()
           next_word+=':start:'
           next_word+=':sudo_opt:'
         else
-          #
+          # Not an option flag; nothing to do.  (If the command line is
+          # syntactically valid, ${this_word//:sudo_opt:/} should be
+          # non-empty now.)
         fi
       elif [[ $this_word == *':sudo_arg:'* ]]; then
         next_word+=':sudo_opt:'