diff --git a/docs/gitbook/usage/how-it-works.md b/docs/gitbook/usage/how-it-works.md
index 45fb5d9e..dbe09b74 100644
--- a/docs/gitbook/usage/how-it-works.md
+++ b/docs/gitbook/usage/how-it-works.md
@@ -120,6 +120,8 @@ in the primary autoscaler when a rollout for the deployment starts and completes
 Optionally, you can create two HPAs, one for canary and one for the primary to update the HPA without
 doing a new rollout. As the canary deployment will be scaled to 0, the HPA on the canary will be inactive.
 
+**Note** Flagger requires `autoscaling/v2` or `autoscaling/v2beta2` API version for HPAs.
+
 The progress deadline represents the maximum time in seconds for the canary deployment to
 make progress before it is rolled back, defaults to ten minutes.