diff --git a/opts/port.go b/opts/port.go
index ef3f12a465..d337cb1a43 100644
--- a/opts/port.go
+++ b/opts/port.go
@@ -16,6 +16,7 @@ const (
 	portOptMode          = "mode"
 )
 
+// PortOpt represents a port config in swarm mode.
 type PortOpt struct {
 	ports []swarm.PortConfig
 }