diff --git a/lib/fluent/test/driver/base.rb b/lib/fluent/test/driver/base.rb
index dfd56ac1a9..b53f863db4 100644
--- a/lib/fluent/test/driver/base.rb
+++ b/lib/fluent/test/driver/base.rb
@@ -173,7 +173,7 @@ def instance_shutdown(log: Logger.new($stdout))
 
           if @socket_manager_server
             @socket_manager_server.close
-            if @socket_manager_server.is_a?(String) && File.exist?(@socket_manager_path)
+            if @socket_manager_path.is_a?(String) && File.exist?(@socket_manager_path)
               FileUtils.rm_f @socket_manager_path
             end
           end
diff --git a/test/plugin_helper/test_server.rb b/test/plugin_helper/test_server.rb
index 3dc308474b..a08734ae46 100644
--- a/test/plugin_helper/test_server.rb
+++ b/test/plugin_helper/test_server.rb
@@ -37,7 +37,7 @@ class Dummy < Fluent::Plugin::TestBase
     (@d.terminated? || @d.terminate) rescue nil
 
     @socket_manager_server.close
-    if @socket_manager_server.is_a?(String) && File.exist?(@socket_manager_path)
+    if @socket_manager_path.is_a?(String) && File.exist?(@socket_manager_path)
       FileUtils.rm_f @socket_manager_path
     end
   end