diff --git a/README.md b/README.md
index 769da6e..9968c6a 100644
--- a/README.md
+++ b/README.md
@@ -168,6 +168,7 @@ This plugin uses internal class of Fluentd, so it's easy to break.
 - `fluentd_tail_file_closed`: Number of closed files
 - `fluentd_tail_file_opened`: Number of opened files
 - `fluentd_tail_file_rotated`: Number of rotated files
+- `fluentd_tail_file_throttled`: Number of throttled files
 
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