diff --git a/lib/fluent/plugin/buf_file.rb b/lib/fluent/plugin/buf_file.rb
index de8a22e0e6..70e086d40d 100644
--- a/lib/fluent/plugin/buf_file.rb
+++ b/lib/fluent/plugin/buf_file.rb
@@ -146,6 +146,8 @@ def resume
           next unless File.file?(path)
 
           if owner.respond_to?(:buffer_config) && owner.buffer_config&.flush_at_shutdown
+            # When `flush_at_shutdown` is `true`, the remaining chunk files during resuming are possibly broken
+            # since there may be a power failure or similar failure.
             log.warn { "restoring buffer file: path = #{path}" }
           else
             log.debug { "restoring buffer file: path = #{path}" }
diff --git a/lib/fluent/plugin/buf_file_single.rb b/lib/fluent/plugin/buf_file_single.rb
index 600f8945f6..1d974962a7 100644
--- a/lib/fluent/plugin/buf_file_single.rb
+++ b/lib/fluent/plugin/buf_file_single.rb
@@ -167,6 +167,8 @@ def resume
           next unless File.file?(path)
 
           if owner.respond_to?(:buffer_config) && owner.buffer_config&.flush_at_shutdown
+            # When `flush_at_shutdown` is `true`, the remaining chunk files during resuming are possibly broken
+            # since there may be a power failure or similar failure.
             log.warn { "restoring buffer file: path = #{path}" }
           else
             log.debug { "restoring buffer file: path = #{path}" }