diff --git a/pulsar/producer.go b/pulsar/producer.go
index 46103b539..a95142638 100644
--- a/pulsar/producer.go
+++ b/pulsar/producer.go
@@ -128,6 +128,8 @@ type Producer interface {
 	Send(context.Context, *ProducerMessage) (MessageID, error)
 
 	// SendAsync a message in asynchronous mode
+	// This call is blocked when the `event channel` becomes full (default: 10) or the
+	// `maxPendingMessages` becomes full (default: 1000)
 	// The callback will report back the message being published and
 	// the eventual error in publishing
 	SendAsync(context.Context, *ProducerMessage, func(MessageID, *ProducerMessage, error))