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:
 
diff --git a/Modules/_io/bytesio.c b/Modules/_io/bytesio.c
index 7b56551..5ca878d 100644
--- a/Modules/_io/bytesio.c
+++ b/Modules/_io/bytesio.c
@@ -759,9 +759,11 @@
 static int
 bytesio_init(bytesio *self, PyObject *args, PyObject *kwds)
 {
+    char *kwlist[] = {"initial_bytes", NULL};
     PyObject *initvalue = NULL;
 
-    if (!PyArg_ParseTuple(args, "|O:BytesIO", &initvalue))
+    if (!PyArg_ParseTupleAndKeywords(args, kwds, "|O:BytesIO", kwlist,
+                                     &initvalue))
         return -1;
 
     /* In case, __init__ is called multiple times. */