diff --git a/lib/puma/null_io.rb b/lib/puma/null_io.rb
index 71d410c6..70f8fe38 100644
--- a/lib/puma/null_io.rb
+++ b/lib/puma/null_io.rb
@@ -52,5 +52,9 @@ module Puma
     def flush
       self
     end
+
+    def closed?
+      true
+    end
   end
 end
diff --git a/test/test_null_io.rb b/test/test_null_io.rb
index 8a8f034b..c76183a1 100644
--- a/test/test_null_io.rb
+++ b/test/test_null_io.rb
@@ -64,4 +64,8 @@ class TestNullIO < Minitest::Test
   def test_flush_returns_self
     assert_equal nio, nio.flush
   end
+
+  def test_closed_returns_true
+    assert_equal true, nio.closed?
+  end
 end