diff --git a/docs/simplesamlphp-upgrade-notes-2.0.md b/docs/simplesamlphp-upgrade-notes-2.0.md
index 1e9be1b1d5cb04153d3bdbecd2b12cdca6f13e0a..80d554f61debfa0fcaa2708f9cb129f5b2ea6fa0 100644
--- a/docs/simplesamlphp-upgrade-notes-2.0.md
+++ b/docs/simplesamlphp-upgrade-notes-2.0.md
@@ -30,6 +30,8 @@ Functional changes
   It is possible to switch back via the `sharedkey_algorithm`.
   Note however that CBC is vulnerable to the Padding oracle attack.
 - All support for the Shibboleth 1.3 / SAML 1.1 protocol has been removed.
+- Sessions are no longer backwards compatible with previous versions. Make sure to clear your session cache during
+  the upgrade process. How to do this depends on your session backend.
 
 Configuration changes
 ---------------------