diff --git a/RELEASE_NOTES.txt b/RELEASE_NOTES.txt
index b9bd1ac..4aaa469 100644
--- a/RELEASE_NOTES.txt
+++ b/RELEASE_NOTES.txt
@@ -6,6 +6,8 @@
 with HttpCore 4.3 and HttpClient 4.3 APIs. Configuration and preference APIs of HttpAsyncClient
 are now consistent with those used by HttpClient 4.3.
 
+Users of previous releases of HttpAsyncClient are advised to upgrade.
+
 Changelog:
 
 * Redesign of configuration and preference APIs.