diff --git a/railties/guides/source/active_support_core_extensions.textile b/railties/guides/source/active_support_core_extensions.textile
index 7a6abf40b6..5393bcc43f 100644
--- a/railties/guides/source/active_support_core_extensions.textile
+++ b/railties/guides/source/active_support_core_extensions.textile
@@ -701,6 +701,8 @@ def raw(stringish)
 end
 </ruby>
 
+NOTE: Defined in +active_support/core_ext/string/output_safety.rb+.
+
 h4. +squish+
 
 The method +String#squish+ strips leading and trailing whitespace, and substitutes runs of whitespace with a single space each: