diff --git a/include/grpc++/impl/codegen/sync_stream.h b/include/grpc++/impl/codegen/sync_stream.h
index 36518abb785..7601ceae92d 100644
--- a/include/grpc++/impl/codegen/sync_stream.h
+++ b/include/grpc++/impl/codegen/sync_stream.h
@@ -69,6 +69,7 @@ class ServerStreamingInterface {
  public:
   virtual ~ServerStreamingInterface() {}
 
+  /// Blocking send initial metadata to client.
   virtual void SendInitialMetadata() = 0;
 };