diff --git a/test/plugin_helper/test_http_server_helper.rb b/test/plugin_helper/test_http_server_helper.rb
index 905526c207..a3f89cde4d 100644
--- a/test/plugin_helper/test_http_server_helper.rb
+++ b/test/plugin_helper/test_http_server_helper.rb
@@ -132,7 +132,7 @@ def start_https_request(addr, port, verify: true, cert_path: nil, selfsigned: tr
     resp = nil
     error = nil
 
-    Async do
+    Sync do
       Console.logger = Fluent::Log::ConsoleAdapter.wrap(NULL_LOGGER)
       begin
         response = yield(client)
@@ -141,7 +141,8 @@ def start_https_request(addr, port, verify: true, cert_path: nil, selfsigned: tr
       end
 
       if response
-        resp = Response.new(response.status.to_s, response.body.read, response.headers)
+        resp = Response.new(response.status.to_s, response.read, response.headers)
+        response.close
       end
     end