diff --git a/stdlib/zlib/0/gzip_writer.rbs b/stdlib/zlib/0/gzip_writer.rbs
index 4f6cc0836..55fd0393d 100644
--- a/stdlib/zlib/0/gzip_writer.rbs
+++ b/stdlib/zlib/0/gzip_writer.rbs
@@ -162,6 +162,6 @@ module Zlib
     # `:external_encoding`, `:internal_encoding` and `:encoding` may be set as in
     # IO::new.
     #
-    def initialize: (_Writer io, ?Integer level, ?Integer strategy, **untyped opts) -> void
+    def initialize: (_Writer io, ?Integer? level, ?Integer? strategy, **untyped opts) -> void
   end
 end