diff --git a/lib/net/imap/config.rb b/lib/net/imap/config.rb
index 4c309f7b..411ce8ef 100644
--- a/lib/net/imap/config.rb
+++ b/lib/net/imap/config.rb
@@ -310,7 +310,7 @@ def self.[](config)
       #
       # * original: +-1+ (_never_ send non-synchronizing literals)
       # * +0.6+: 16 KiB
-      attr_accessor :max_non_synchronizing_literal, type: Integer?, defaults: {
+      attr_accessor :max_non_synchronizing_literal, type: Integer, defaults: {
         0.0r => -1,
         0.6r => 16 << 16, # 16 KiB
       }