diff --git a/test/zlib/test_zlib.rb b/test/zlib/test_zlib.rb
index 06e85f6315..68acc72d9e 100644
--- a/test/zlib/test_zlib.rb
+++ b/test/zlib/test_zlib.rb
@@ -213,7 +213,9 @@ if defined? Zlib
       z = Zlib::Deflate.new
       z << "foo"
       assert_raise(Zlib::StreamError) { z.set_dictionary("foo") }
-      z.close # without this, outputs `zlib(finalizer): the stream was freed prematurely.'
+      EnvUtil.suppress_warning do
+        z.close # without this, outputs `zlib(finalizer): the stream was freed prematurely.'
+      end
     end
 
     def test_reset