diff --git a/guides/source/active_support_core_extensions.md b/guides/source/active_support_core_extensions.md
index 965de0c7611292a692c78396ad093e8ea28f026b..88d651e13cc8cfd22c007a8fa244f63a718dd0d7 100644
--- a/guides/source/active_support_core_extensions.md
+++ b/guides/source/active_support_core_extensions.md
@@ -162,7 +162,7 @@ Active Support provides `duplicable?` to programmatically query an object about
 false.duplicable? # => false
 ```
 
-By definition all objects are `duplicable?` except `nil`, `false`, `true`, symbols, numbers, class, and module objects.
+By definition all objects are `duplicable?` except `nil`, `false`, `true`, symbols, numbers, and class, module, and method objects.
 
 WARNING: Any class can disallow duplication by removing `dup` and `clone` or raising exceptions from them. Thus only `rescue` can tell whether a given arbitrary object is duplicable. `duplicable?` depends on the hard-coded list above, but it is much faster than `rescue`. Use it only if you know the hard-coded list is enough in your use case.