diff --git a/lib/net/imap/response_parser/parser_utils.rb b/lib/net/imap/response_parser/parser_utils.rb
index 99626d033..9c07c8b9c 100644
--- a/lib/net/imap/response_parser/parser_utils.rb
+++ b/lib/net/imap/response_parser/parser_utils.rb
@@ -186,7 +186,7 @@ def peek_str?(str)
         end
 
         def peek_re?(re)
-          assert_no_lookahead if Net::IMAP.debug
+          assert_no_lookahead if config.debug?
           re.match?(@str, @pos)
         end