diff --git a/activesupport/lib/active_support/core_ext/string/output_safety.rb b/activesupport/lib/active_support/core_ext/string/output_safety.rb
index b53929c2a3d1da1bcbb7939595f3e3e6978c30d1..e6f13ec12a3eefa9ad9622d5c0158c753d4ae503 100644
--- a/activesupport/lib/active_support/core_ext/string/output_safety.rb
+++ b/activesupport/lib/active_support/core_ext/string/output_safety.rb
@@ -35,10 +35,16 @@ def html_escape(s)
     # A utility method for escaping HTML entities in JSON strings.
     # This method is also aliased as <tt>j</tt>.
     #
+    # Note that after this operation is performed the output is not
+    # a valid JSON.
+    #
     # In your ERb templates, use this method to escape any HTML entities:
     #   <%=j @person.to_json %>
     #
     # ==== Example:
+    #   puts json_escape("{\"name\":\"john\",\"created_at\":\"2010-04-28T01:39:31Z\",\"id\":1}")
+    #   # => {name:john,created_at:2010-04-28T01:39:31Z,id:1}
+    #
     #   puts json_escape("is a > 0 & a < 10?")
     #   # => is a \u003E 0 \u0026 a \u003C 10?
     def json_escape(s)