diff --git a/lib/fluent/engine.rb b/lib/fluent/engine.rb
index 6074a54592..184cb328d1 100644
--- a/lib/fluent/engine.rb
+++ b/lib/fluent/engine.rb
@@ -79,38 +79,27 @@ def parse_config(io, fname, basepath = Dir.pwd, v1_config = false)
 
     def run_configure(conf)
       configure(conf)
-      conf.check_not_fetched { |key, e|
+      conf.check_not_fetched do |key, e|
         parent_name, plugin_name = e.unused_in
-        if parent_name
-          message = if plugin_name
-                      "section <#{e.name}> is not used in <#{parent_name}> of #{plugin_name} plugin"
-                    else
-                      "section <#{e.name}> is not used in <#{parent_name}>"
-                    end
-
-          if @dry_run_mode && @supervisor_mode
-            $log.warn :supervisor, message
-          elsif e.for_every_workers?
-            $log.warn :worker0, message
-          elsif e.for_this_worker?
-            $log.warn message
-          end
-          next
+        message = if parent_name && plugin_name
+                    "section <#{e.name}> is not used in <#{parent_name}> of #{plugin_name} plugin"
+                  elsif parent_name
+                    "section <#{e.name}> is not used in <#{parent_name}>"
+                  elsif e.name != 'system' && !(@without_source && e.name == 'source')
+                    "parameter '#{key}' in #{e.to_s.strip} is not used."
+                  else
+                    nil
+                  end
+        next if message.nil?
+
+        if @dry_run_mode && @supervisor_mode
+          $log.warn :supervisor, message
+        elsif e.for_every_workers?
+          $log.warn :worker0, message
+        elsif e.for_this_worker?
+          $log.warn message
         end
-
-        unless e.name == 'system'
-          unless @without_source && e.name == 'source'
-            message = "parameter '#{key}' in #{e.to_s.strip} is not used."
-            if @dry_run_mode && @supervisor_mode
-              $log.warn :supervisor, message
-            elsif e.for_every_workers?
-              $log.warn :worker0, message
-            elsif e.for_this_worker?
-              $log.warn message
-            end
-          end
-        end
-      }
+      end
     end
 
     def configure(conf)