diff --git a/test/test_supervisor.rb b/test/test_supervisor.rb
index 875c443c37..b2b9b76dca 100644
--- a/test/test_supervisor.rb
+++ b/test/test_supervisor.rb
@@ -226,27 +226,34 @@ def test_fluentsigdump_get_path_with_pid(data)
   def test_supervisor_event_dump_windows
     omit "Only for Windows, alternative to UNIX signals" unless Fluent.windows?
 
-    ENV['SIGDUMP_PATH'] = TMP_DIR + "/sigdump.log"
-
     server = DummyServer.new
     def server.config
       {:signame => "TestFluentdEvent"}
     end
     server.install_windows_event_handler
-    begin
-      sleep 0.1 # Wait for starting windows event thread
-      event = Win32::Event.open("TestFluentdEvent_CONT")
-      event.set
-      event.close
-      sleep 1.0 # Wait for dumping
-    ensure
-      server.stop_windows_event_thread
-    end
 
-    result_filepaths = Dir.glob("#{TMP_DIR}/*")
-    assert {result_filepaths.length > 0}
-  ensure
-    ENV.delete('SIGDUMP_PATH')
+    assert_rr do
+      # Have to use mock because `Sigdump.dump` seems to be somehow incompatible with RR.
+      # The `mock(server).restart(true) { nil }` line in `test_rpc_server_windows` cause the next error.
+      # Failure: test_supervisor_event_dump_windows(SupervisorTest):
+      #   class()
+      #   Called 0 times.
+      #   Expected 1 times.
+      # .../Ruby26-x64/lib/ruby/gems/2.6.0/gems/sigdump-0.2.4/lib/sigdump.rb:74:in `block in dump_object_count'
+      #     73: ObjectSpace.each_object {|o|
+      #     74:   c = o.class <-- HERE!
+      mock(Sigdump).dump(anything)
+
+      begin
+        sleep 0.1 # Wait for starting windows event thread
+        event = Win32::Event.open("TestFluentdEvent_CONT")
+        event.set
+        event.close
+        sleep 1.0 # Wait for dumping
+      ensure
+        server.stop_windows_event_thread
+      end
+    end
   end
 
   data(:ipv4 => ["0.0.0.0", "127.0.0.1", false],