diff --git a/test/net/imap/test_imap_response_parser.rb b/test/net/imap/test_imap_response_parser.rb
index 2eeaea04f0..f106e4a61d 100644
--- a/test/net/imap/test_imap_response_parser.rb
+++ b/test/net/imap/test_imap_response_parser.rb
@@ -61,6 +61,6 @@ EOF
     response = parser.parse(<<EOF.gsub(/\n/, "\r\n").taint)
 * OK [CLOSED] Previous mailbox closed.
 EOF
-    assert_equal nil, response
+    assert_equal "CLOSED", response.data.code.name
   end
 end