diff --git a/guides/source/active_support_instrumentation.md b/guides/source/active_support_instrumentation.md
index 0fd0112c9f..03af3cf819 100644
--- a/guides/source/active_support_instrumentation.md
+++ b/guides/source/active_support_instrumentation.md
@@ -112,6 +112,7 @@ Action Controller
 | `:controller` | The controller name                                       |
 | `:action`     | The action                                                |
 | `:params`     | Hash of request parameters without any filtered parameter |
+| `:headers`    | Request headers                                           |
 | `:format`     | html/js/json/xml etc                                      |
 | `:method`     | HTTP request verb                                         |
 | `:path`       | Request path                                              |
@@ -121,6 +122,7 @@ Action Controller
   controller: "PostsController",
   action: "new",
   params: { "action" => "new", "controller" => "posts" },
+  headers: #<ActionDispatch::Http::Headers:0x0055a67a519b88>,
   format: :html,
   method: "GET",
   path: "/posts/new"
@@ -134,6 +136,7 @@ Action Controller
 | `:controller`   | The controller name                                       |
 | `:action`       | The action                                                |
 | `:params`       | Hash of request parameters without any filtered parameter |
+| `:headers`      | Request headers                                           |
 | `:format`       | html/js/json/xml etc                                      |
 | `:method`       | HTTP request verb                                         |
 | `:path`         | Request path                                              |
@@ -146,6 +149,7 @@ Action Controller
   controller: "PostsController",
   action: "index",
   params: {"action" => "index", "controller" => "posts"},
+  headers: #<ActionDispatch::Http::Headers:0x0055a67a519b88>,
   format: :html,
   method: "GET",
   path: "/posts",