diff --git a/lib/fluent/plugin/buffer.rb b/lib/fluent/plugin/buffer.rb
index f62e92a713..72bf65c840 100644
--- a/lib/fluent/plugin/buffer.rb
+++ b/lib/fluent/plugin/buffer.rb
@@ -325,8 +325,8 @@ def enqueue_chunk(metadata)
             synchronize do
               @queue << chunk
               @queued_num[metadata] = @queued_num.fetch(metadata, 0) + 1
+              chunk.enqueued!
             end
-            chunk.enqueued!
           end
         end
         bytesize = chunk.bytesize