diff --git a/lib/fluent/plugin/out_relabel.rb b/lib/fluent/plugin/out_relabel.rb
index 28fbfabcdc..3ee74f1b69 100644
--- a/lib/fluent/plugin/out_relabel.rb
+++ b/lib/fluent/plugin/out_relabel.rb
@@ -28,5 +28,10 @@ def multi_workers_ready?
     def process(tag, es)
       router.emit_stream(tag, es)
     end
+
+    def write(chunk)
+      return if chunk.empty?
+      router.emit_stream(chunk.metadata.tag, Fluent::MessagePackEventStream.new(chunk.read))
+    end
   end
 end
diff --git a/lib/fluent/plugin/output.rb b/lib/fluent/plugin/output.rb
index 0aed67db95..8aa4fc8522 100644
--- a/lib/fluent/plugin/output.rb
+++ b/lib/fluent/plugin/output.rb
@@ -1384,6 +1384,7 @@ def retry_state(randomize)
       end
 
       def submit_flush_once
+        return unless @buffer_config.flush_thread_count > 0
         # Without locks: it is rough but enough to select "next" writer selection
         @output_flush_thread_current_position = (@output_flush_thread_current_position + 1) % @buffer_config.flush_thread_count
         state = @output_flush_threads[@output_flush_thread_current_position]