diff --git a/internal/indexnode/errors.go b/internal/indexnode/errors.go
index 8fdaa61952..986762e094 100644
--- a/internal/indexnode/errors.go
+++ b/internal/indexnode/errors.go
@@ -25,6 +25,7 @@ func msgIndexNodeIsUnhealthy(nodeID UniqueID) string {
 	return fmt.Sprintf("index node %d is not ready", nodeID)
 }
 
+// errIndexNodeIsUnhealthy return an error that specified IndexNode is not healthy.
 func errIndexNodeIsUnhealthy(nodeID UniqueID) error {
 	return errors.New(msgIndexNodeIsUnhealthy(nodeID))
 }