diff --git a/documentation/migratingToV5.md b/documentation/migratingToV5.md
index a02cfb0..1deca60 100644
--- a/documentation/migratingToV5.md
+++ b/documentation/migratingToV5.md
@@ -64,4 +64,9 @@ machine
 
 Make sure you use the correct `StateMachineDefinitionBuilder`:
 - from namespace `Appccelerate.StateMachine.Machine` for state machines **without** async/await support
-- from namespace `Appccelerate.StateMachine.AsyncMachine` for state machines **with** async/await support
\ No newline at end of file
+- from namespace `Appccelerate.StateMachine.AsyncMachine` for state machines **with** async/await support
+
+## Changes in extension API
+
+The extension API is changed in version 5, too.
+Instead of mutable states, the state definition is passed to the extensions.
\ No newline at end of file