diff --git a/README.md b/README.md
index b8d1616c..b577370a 100644
--- a/README.md
+++ b/README.md
@@ -8,6 +8,8 @@ This Java client helps connecting to an ACME server, and performing all necessar
 
 It is an independent open source implementation that is not affiliated with or endorsed by _Let's Encrypt_.
 
+**Note:** Make sure to use _acme4j_ 2.5 or higher, before November 1st 2019. Due to a change in the ACME protocol, _acme4j_ < 2.5 will fail to connect to servers after that date. _acme4j_ v1 is not affected. See [here](https://community.letsencrypt.org/t/acme-v2-scheduled-deprecation-of-unauthenticated-resource-gets/74380) for details.
+
 ## Features
 
 * Fully supports the ACME v2 protocol up to [draft 16](https://tools.ietf.org/html/draft-ietf-acme-acme-16)
diff --git a/src/site/markdown/index.md.vm b/src/site/markdown/index.md.vm
index 9a78cdf9..1654850d 100644
--- a/src/site/markdown/index.md.vm
+++ b/src/site/markdown/index.md.vm
@@ -11,6 +11,11 @@ It is an independent open source implementation that is not affiliated with or e
 
 The source code can be found at [GitHub](https://github.com/shred/acme4j) and is distributed under the terms of [Apache License 2.0](http://www.apache.org/licenses/LICENSE-2.0).
 
+<div class="alert alert-info" role="alert">
+
+**Note:** Make sure to use _acme4j_ 2.5 or higher, before November 1st 2019. Due to a change in the ACME protocol, _acme4j_ < 2.5 will fail to connect to servers after that date. _acme4j_ v1 is not affected. See [here](https://community.letsencrypt.org/t/acme-v2-scheduled-deprecation-of-unauthenticated-resource-gets/74380) for details.
+</div>
+
 Quick Start
 -----------