diff --git a/lib/fluent/plugin/buffer.rb b/lib/fluent/plugin/buffer.rb
index aac191e63c..5be2c45c34 100644
--- a/lib/fluent/plugin/buffer.rb
+++ b/lib/fluent/plugin/buffer.rb
@@ -319,6 +319,8 @@ def enqueue_chunk(metadata)
         return nil unless chunk
 
         chunk.synchronize do
+          return nil if chunk.queued?
+
           if chunk.empty?
             chunk.close
           else