diff --git a/Lib/fontTools/subset/__init__.py b/Lib/fontTools/subset/__init__.py
index c32e6fe05..5a1af9a6c 100644
--- a/Lib/fontTools/subset/__init__.py
+++ b/Lib/fontTools/subset/__init__.py
@@ -122,7 +122,8 @@ Other options
 ^^^^^^^^^^^^^
 
 For the other options listed below, to see the current value of the option,
-pass a value of '?' to it, with or without a '='.
+pass a value of '?' to it, with or without a '='. In some environments,
+you might need to escape the question mark, like this: '--glyph-names\?'.
 
 Examples::