diff --git a/lib/fluent/plugin/base.rb b/lib/fluent/plugin/base.rb
index 3bd8f44224..ebd5786e2b 100644
--- a/lib/fluent/plugin/base.rb
+++ b/lib/fluent/plugin/base.rb
@@ -54,12 +54,9 @@ def fluentd_worker_id
 
       def configure(conf)
         if Fluent::Engine.supervisor_mode || (conf.respond_to?(:for_this_worker?) && conf.for_this_worker?)
-          workers = if conf.target_worker_ids && !conf.target_worker_ids.empty?
-                      conf.target_worker_ids.size
-                    else
-                      1
-                    end
-          system_config_override(workers: workers)
+          if !conf&.target_worker_ids&.empty?
+            system_config_override(workers: conf.target_worker_ids.size)
+          end
         end
         super(conf, system_config.strict_config_value)
         @_state ||= State.new(false, false, false, false, false, false, false, false, false)