diff --git a/Lib/test/test_memoryio.py b/Lib/test/test_memoryio.py
index 7dd1658..6ab8328 100644
--- a/Lib/test/test_memoryio.py
+++ b/Lib/test/test_memoryio.py
@@ -461,6 +461,11 @@
         self.assertEqual(memio.write(a), 10)
         self.assertEqual(memio.getvalue(), buf)
 
+    def test_issue5449(self):
+        buf = self.buftype("1234567890")
+        self.ioclass(initial_bytes=buf)
+        self.assertRaises(TypeError, self.ioclass, buf, foo=None)
+
 
 class TextIOTestMixin: