diff --git a/activemodel/lib/active_model/serialization.rb b/activemodel/lib/active_model/serialization.rb
index 00cd05b7ef..3751e4a741 100644
--- a/activemodel/lib/active_model/serialization.rb
+++ b/activemodel/lib/active_model/serialization.rb
@@ -64,7 +64,7 @@ module ActiveModel
   #   person.to_json             # => "{\"name\":\"Bob\"}"
   #   person.to_xml              # => "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<serial-person...
   #
-  # Valid options are <tt>:only</tt>, <tt>:except</tt>, <tt>:methods</tt> and <tt>include</tt>.
+  # Valid options are <tt>:only</tt>, <tt>:except</tt>, <tt>:methods</tt> and <tt>:include</tt>.
   # The following are all valid examples:
   #
   #   person.serializable_hash(:only => 'name')