diff --git a/docs/design/horizontal-pod-autoscaler.md b/docs/design/horizontal-pod-autoscaler.md
index 1b0d78bd558..d8d2280f5bf 100644
--- a/docs/design/horizontal-pod-autoscaler.md
+++ b/docs/design/horizontal-pod-autoscaler.md
@@ -32,6 +32,8 @@ Documentation for other releases can be found at
 
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+<h2>Warning! This document might be outdated.</h2>
+
 # Horizontal Pod Autoscaling
 
 ## Preface