diff --git a/node/src/main/kotlin/net/corda/node/internal/FlowSafeSubject.kt b/node/src/main/kotlin/net/corda/node/internal/FlowSafeSubject.kt
index 5336298a03..4570c8f653 100644
--- a/node/src/main/kotlin/net/corda/node/internal/FlowSafeSubject.kt
+++ b/node/src/main/kotlin/net/corda/node/internal/FlowSafeSubject.kt
@@ -14,10 +14,17 @@ import rx.subjects.Subject
  *
  * Upon [rx.Observable.subscribe] it will wrap everything that is a non [SafeSubscriber] with a [FlowSafeSubscriber] the same way
  * [rx.subjects.PublishSubject] wraps everything that is a non [SafeSubscriber] with a [SafeSubscriber].
+ *
+ * In case we need to subscribe with a [SafeSubscriber] to a [FlowSafeSubject], we have to:
+ * 1. Declare a custom Subscriber that will extend [SafeSubscriber].
+ * 2. Wrap with the custom Subscriber the [rx.Observer] to be subscribed to [FlowSafeSubject].
+ * 3. Subscribe to [FlowSafeSubject] passing the custom Subscriber.
  */
 @VisibleForTesting
 class FlowSafeSubject<T, R>(private val actual: Subject<T, R>) : Observer<T> by actual,
     Subject<T, R>(OnSubscribe<R> { subscriber ->
+        // we used '==' instead of 'is', so that we replace only instances of SafeSubscriber with FlowSafeSubscriber,
+        // but leave untouched instances of a classes extending SafeSubscriber. That way, we allow subscribing SafeSubscribers.
         if (subscriber::class == SafeSubscriber::class) {
             actual.unsafeSubscribe(FlowSafeSubscriber((subscriber as SafeSubscriber).actual))
         } else {