diff --git a/lib/fluent/plugin_helper/cert_option.rb b/lib/fluent/plugin_helper/cert_option.rb
index 270917d327..8702f772c7 100644
--- a/lib/fluent/plugin_helper/cert_option.rb
+++ b/lib/fluent/plugin_helper/cert_option.rb
@@ -33,6 +33,8 @@ def cert_option_create_context(version, insecure, ciphers, conf)
 
         if conf.client_cert_auth
           ctx.verify_mode = OpenSSL::SSL::VERIFY_PEER | OpenSSL::SSL::VERIFY_FAIL_IF_NO_PEER_CERT
+        else
+          ctx.verify_mode = OpenSSL::SSL::VERIFY_NONE
         end
 
         ctx.ca_file = conf.ca_path