diff --git a/node/src/main/kotlin/com/r3corda/node/services/statemachine/StateMachineManager.kt b/node/src/main/kotlin/com/r3corda/node/services/statemachine/StateMachineManager.kt
index 877a09af26..cd8d74da65 100644
--- a/node/src/main/kotlin/com/r3corda/node/services/statemachine/StateMachineManager.kt
+++ b/node/src/main/kotlin/com/r3corda/node/services/statemachine/StateMachineManager.kt
@@ -91,6 +91,10 @@ class StateMachineManager(val serviceHub: ServiceHubInternal, tokenizableService
 
     private val _changesPublisher = PublishSubject.create<Triple<ProtocolLogic<*>, AddOrRemove, Long>>()
 
+    /**
+     * An observable that emits triples of the changing protocol, the type of change, and a process-specific ID number
+     * which may change across restarts.
+     */
     val changes: Observable<Triple<ProtocolLogic<*>, AddOrRemove, Long>>
         get() = _changesPublisher