diff --git a/main.py b/main.py
index 5733dec..a0f44d5 100755
--- a/main.py
+++ b/main.py
@@ -228,6 +228,8 @@ and have no effect if --prenodef is specified.
 If filename is a dash (-) then standard input is used.
 Use: {progname} -O help for help on the optimizer control options.
 
+Comments are always removed in the output, even when using --prettify.
+
 Preprocessor modes:
     ext       Invoke a preprocessor with no default parameters
     mcpp      Invoke mcpp as preprocessor, setting default parameters pertinent